Encoder, decoder, encoding method, and decoding method

ABSTRACT

An encoder includes circuitry and memory coupled to the circuitry. In operation, the circuitry: performs quantization on a plurality of transform coefficients of a current block to be encoded, using a quantization matrix when orthogonal transform is performed on the current block and secondary transform is not performed on the current block; and performs quantization on the plurality of transform coefficients of the current block without using the quantization matrix when orthogonal transform is not performed on the current block and when both orthogonal transform and secondary transform are performed on the current block.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of U.S. Pat.Application No. 17/377,107 filed on Jul. 15, 2021, which is a U.S.continuation application of PCT International Patent Application NumberPCT/JP2020/008531 filed on Feb. 28, 2020, claiming the benefit ofpriority of U.S. Provisional Pat. Application No. 62/812501 filed onMar. 1, 2019, and the benefit of priority of U.S. Provisional Pat.Application No. 62/819914 filed on Mar. 18, 2019, the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to video coding, and relates to, forexample, a system, a constituent element, a method, etc., in encodingand decoding of videos.

2. Description of the Related Art

The video coding technology has been developed from H.261 and MPEG-1 toH.264/AVC (Advanced Video Coding), MPEG-LA, H.265 (ISO/IEC 23008-2 GEVC)/ HEVC (High Efficiency Video Coding), and H.266/VVC (Versatile VideoCodec). With this development, it is always required to improve andoptimize video coding technology in order to process digital video datathe amount of which has kept increasing in various kinds ofapplications.

It is to be noted that H.265/HEVC relates to one example of aconventional standard related to the above-described video codingtechnology.

SUMMARY

For example, an encoder according to an aspect of the present disclosureincludes circuitry and memory coupled to the circuitry. In operation,the circuitry: performs quantization on a plurality of transformcoefficients of a current block to be encoded, using a quantizationmatrix when orthogonal transform is performed on the current block andsecondary transform is not performed on the current block; and performsquantization on the plurality of transform coefficients of the currentblock without using the quantization matrix when orthogonal transform isnot performed on the current block and when both orthogonal transformand secondary transform are performed on the current block.

Some of implementations of embodiments according to the presentdisclosure may: improve a coding efficiency; simplify encoding/decoding;increase an encoding/decoding speed; and efficiently select appropriateconstituent elements and/or operations to be used in encoding anddecoding, such as appropriate filters, block sizes, motion vectors,reference pictures, reference blocks, etc.

Further advantages and effects according to one aspect of the presentdisclosure will become apparent from the Specification and the Drawings.These advantages and/or effects are obtainable by some embodiments andfeatures described in the Specification and the Drawings. However, notall of the features always need to be provided to obtain one or moreadvantages and/or effects.

It is to be noted that these general or specific aspects may beimplemented using a system, a method, an integrated circuit, a computerprogram, or a recording medium, or any combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a configuration of an encoderaccording to an embodiment;

FIG. 2 is a flow chart indicating one example of an overall encodingprocess performed by the encoder;

FIG. 3 is a conceptual diagram illustrating one example of blocksplitting;

FIG. 4A is a conceptual diagram illustrating one example of a sliceconfiguration;

FIG. 4B is a conceptual diagram illustrating one example of a tileconfiguration;

FIG. 5A is a chart indicating transform basis functions for varioustransform types;

FIG. 5B is a conceptual diagram illustrating example spatially varyingtransforms (SVT);

FIG. 6A is a conceptual diagram illustrating one example of a filtershape used in an adaptive loop filter (ALF);

FIG. 6B is a conceptual diagram illustrating another example of a filtershape used in an ALF;

FIG. 6C is a conceptual diagram illustrating another example of a filtershape used in an ALF;

FIG. 7 is a block diagram indicating one example of a specificconfiguration of a loop filter which functions as a deblocking filter(DBF);

FIG. 8 is a conceptual diagram indicating an example of a deblockingfilter having a symmetrical filtering characteristic with respect to ablock boundary;

FIG. 9 is a conceptual diagram for illustrating a block boundary onwhich a deblocking filter process is performed;

FIG. 10 is a conceptual diagram indicating examples of Bs values;

FIG. 11 is a flow chart illustrating one example of a process performedby a prediction processor of the encoder;

FIG. 12 is a flow chart illustrating another example of a processperformed by the prediction processor of the encoder;

FIG. 13 is a flow chart illustrating another example of a processperformed by the prediction processor of the encoder;

FIG. 14 is a conceptual diagram illustrating sixty-seven intraprediction modes used in intra prediction in an embodiment;

FIG. 15 is a flow chart illustrating an example basic processing flow ofinter prediction;

FIG. 16 is a flow chart illustrating one example of derivation of motionvectors;

FIG. 17 is a flow chart illustrating another example of derivation ofmotion vectors;

FIG. 18 is a flow chart illustrating another example of derivation ofmotion vectors;

FIG. 19 is a flow chart illustrating an example of inter prediction innormal inter mode;

FIG. 20 is a flow chart illustrating an example of inter prediction inmerge mode;

FIG. 21 is a conceptual diagram for illustrating one example of a motionvector derivation process in merge mode;

FIG. 22 is a flow chart illustrating one example of frame rate upconversion (FRUC) process;

FIG. 23 is a conceptual diagram for illustrating one example of patternmatching (bilateral matching) between two blocks along a motiontrajectory;

FIG. 24 is a conceptual diagram for illustrating one example of patternmatching (template matching) between a template in a current picture anda block in a reference picture;

FIG. 25A is a conceptual diagram for illustrating one example ofderiving a motion vector of each sub-block based on motion vectors of aplurality of neighboring blocks;

FIG. 25B is a conceptual diagram for illustrating one example ofderiving a motion vector of each sub-block in affine mode in which threecontrol points are used;

FIG. 26A is a conceptual diagram for illustrating an affine merge mode;

FIG. 26B is a conceptual diagram for illustrating an affine merge modein which two control points are used;

FIG. 26C is a conceptual diagram for illustrating an affine merge modein which three control points are used;

FIG. 27 is a flow chart illustrating one example of a process in affinemerge mode;

FIG. 28A is a conceptual diagram for illustrating an affine inter modein which two control points are used;

FIG. 28B is a conceptual diagram for illustrating an affine inter modein which three control points are used;

FIG. 29 is a flow chart illustrating one example of a process in affineinter mode;

FIG. 30A is a conceptual diagram for illustrating an affine inter modein which a current block has three control points and a neighboringblock has two control points;

FIG. 30B is a conceptual diagram for illustrating an affine inter modein which a current block has two control points and a neighboring blockhas three control points;

FIG. 31A is a flow chart illustrating a merge mode process includingdecoder motion vector refinement (DMVR);

FIG. 31B is a conceptual diagram for illustrating one example of a DMVRprocess;

FIG. 32 is a flow chart illustrating one example of generation of aprediction image;

FIG. 33 is a flow chart illustrating another example of generation of aprediction image;

FIG. 34 is a flow chart illustrating another example of generation of aprediction image;

FIG. 35 is a flow chart illustrating one example of a prediction imagecorrection process performed by an overlapped block motion compensation(OBMC) process;

FIG. 36 is a conceptual diagram for illustrating one example of aprediction image correction process performed by an OBMC process;

FIG. 37 is a conceptual diagram for illustrating generation of twotriangular prediction images;

FIG. 38 is a conceptual diagram for illustrating a model assuminguniform linear motion;

FIG. 39 is a conceptual diagram for illustrating one example of aprediction image generation method using a luminance correction processperformed by a local illumination compensation (LIC) process;

FIG. 40 is a block diagram illustrating a mounting example of theencoder;

FIG. 41 is a block diagram illustrating a configuration of a decoderaccording to an embodiment;

FIG. 42 is a flow chart illustrating one example of an overall decodingprocess performed by the decoder;

FIG. 43 is a flow chart illustrating one example of a process performedby a prediction processor of the decoder;

FIG. 44 is a flow chart illustrating another example of a processperformed by the prediction processor of the decoder;

FIG. 45 is a flow chart illustrating an example of inter prediction innormal inter mode in the decoder;

FIG. 46 is a block diagram illustrating a mounting example of thedecoder;

FIG. 47 is a flow chart indicating one example of an operation inquantization processing performed by an encoder according to Aspect 1;

FIG. 48 is a flow chart indicating one example of an operation ininverse quantization processing performed by a decoder according toAspect 1;

FIG. 49 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in an encoder according to Aspect 2;

FIG. 50 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in a decoder according to Aspect 2;

FIG. 51 is a diagram for explaining a first example of generating a QMfor a rectangular block based on a QM for a square block in Step S102 inFIG. 49 and in Step S202 in FIG. 50 ;

FIG. 52 is a diagram for explaining a method of generating the QM forthe rectangular block explained with reference to FIG. 51 bydown-converting the corresponding QM for the square block;

FIG. 53 is a diagram for explaining a second example of generating a QMfor a rectangular block based on a QM for a square block in Step S102 inFIG. 49 and in Step S202 in FIG. 50 ;

FIG. 54 is a diagram for explaining a method of generating the QM forthe rectangular block explained with reference to FIG. 53 byup-converting the corresponding QM for the square block;

FIG. 55 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in an encoder according to Aspect 3;

FIG. 56 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in a decoder according to Aspect 3;

FIG. 57 is a diagram for explaining an example of generating, for eachof blocks which have various sizes, a QM corresponding to the size of aneffective transform coefficient domain in the block, in each of StepS301 in FIG. 55 and in Step S401 in FIG. 56 ;

FIG. 58 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in an encoder according to a variationof Aspect 3;

FIG. 59 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in a decoder according to the variationof Aspect 3;

FIG. 60 is a diagram for explaining a first example of generating a QMfor a rectangular block based on a QM for a square block in Step S502 inFIG. 58 and in Step S602 in FIG. 59 ;

FIG. 61 is a diagram for explaining a method of generating the QM forthe rectangular block explained with reference to FIG. 60 bydown-converting the corresponding QM for the square block;

FIG. 62 is a diagram for explaining a second example of generating a QMfor a rectangular block based on a QM for a square block in Step S502 inFIG. 58 and in Step S602 in FIG. 59 ;

FIG. 63 is a diagram for explaining a method of generating the QM forthe rectangular block with reference to FIG. 62 by up-converting thecorresponding QM for the square block;

FIG. 64 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in an encoder according to Aspect 4;

FIG. 65 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in a decoder according to Aspect 4;

FIG. 66 is a diagram for explaining one example of generating, in eachof Step S701 in FIG. 64 and in Step S801 in FIG. 65 , a QM for a currentblock to be processed having one of various block sizes, based on valuesof quantized coefficients of a QM having only diagonal components in thecurrent block using a common method;

FIG. 67 is a diagram for explaining another example of generating, ineach of Step S701 in FIG. 64 and in Step S801 in FIG. 65 , a QM for acurrent block to be processed having one of various block sizes, basedon values of quantized coefficients of a QM having only diagonalcomponents in the current block using a common method;

FIG. 68 is a block diagram illustrating an overall configuration of acontent providing system for implementing a content distributionservice;

FIG. 69 is a conceptual diagram illustrating one example of an encodingstructure in scalable encoding;

FIG. 70 is a conceptual diagram illustrating one example of an encodingstructure in scalable encoding;

FIG. 71 is a conceptual diagram illustrating an example of a displayscreen of a web page;

FIG. 72 is a conceptual diagram illustrating an example of a displayscreen of a web page;

FIG. 73 is a block diagram illustrating one example of a smartphone; and

FIG. 74 is a block diagram illustrating an example of a configuration ofa smartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For example, an encoder according to an aspect of the present disclosureincludes circuitry and memory coupled to the circuitry. In operation,the circuitry: performs quantization on a plurality of transformcoefficients of a current block to be encoded, using a quantizationmatrix when orthogonal transform is performed on the current block andsecondary transform is not performed on the current block; and performsquantization on the plurality of transform coefficients of the currentblock without using the quantization matrix when orthogonal transform isnot performed on the current block and when both orthogonal transformand secondary transform are performed on the current block.

In this way, the encoder performs quantization, without using thequantization matrix, on the current block for which a sufficient effectof adjusting a subjective image quality may not be obtained even if thequantization matrix is applied, which reduces the processing amount.Furthermore, the encoder is capable of appropriately applying thequantization matrix to a plurality of prediction residuals of theorthogonal-transformed current block, which provides an effect ofadjusting the subjective image quality. Accordingly, the encoder iscapable of increasing the coding efficiency while reducing decrease insubjective image quality, both in a case in which the quantizationmatrix is applied and in a case in which the quantization matrix is notapplied.

For example, the circuitry may determine whether to use the quantizationmatrix in the quantization on the current block, based on informationindicating whether orthogonal transform has been performed on thecurrent block and whether secondary transform has been performed on theplurality of transform coefficients of the current block.

In this way, the encoder is capable of appropriately determining whetherto apply the quantization matrix to the current block in thequantization processing, and thus is capable of increasing the codingefficiency while reducing decrease in subjective image quality.

For example, when the current block is a rectangular block, thecircuitry may: generate a second quantization matrix for the pluralityof transform coefficients of the rectangular block by converting a firstquantization matrix for a plurality of transform coefficients of asquare block; and perform quantization on the plurality of transformcoefficient of the rectangular block, using the second quantizationmatrix.

In this way, the encoder is capable of generating the quantizationmatrix corresponding to the rectangular block based on the quantizationmatrix corresponding to the square block, and thus there is no need forthe encoder to encode a quantization matrix corresponding to therectangular block. Furthermore, the encoder is capable of using theappropriate quantization matrix also for the rectangular block withoutincreasing the amount of codes. Accordingly, the encoder is capable ofefficiently quantizing rectangular blocks which have various shapes, andthus is capable of increasing the coding efficiency.

Furthermore, a decoder according to an aspect of the present disclosureincludes circuitry and memory coupled to the circuitry. In operation,the circuitry: performs inverse quantization on a plurality of transformcoefficients of a current block to be decoded, using a quantizationmatrix when inverse orthogonal transform is performed on the currentblock and inverse secondary transform is not performed on the currentblock; and performs inverse quantization on the plurality of transformcoefficients of the current block without using the quantization matrixwhen inverse orthogonal transform is not performed on the current blockand when both inverse orthogonal transform and inverse secondarytransform are performed on the current block.

In this way, the decoder performs inverse quantization, without usingthe quantization matrix, on the current block for which a sufficienteffect of adjusting a subjective image quality may not be obtained evenif the quantization matrix is applied, which reduces the processingamount. Furthermore, the decoder is capable of appropriately applyingthe quantization matrix for the current block on which orthogonaltransform, quantization, and encoding have been performed, whichprovides an effect of adjusting the subjective image quality.Accordingly, the decoder is capable of increasing the processingefficiency while reducing decrease in subjective image quality, both inthe case in which the quantization matrix is applied and in the case inwhich the quantization matrix is not applied.

For example, the circuitry may determine whether to use the quantizationmatrix in the inverse quantization on the current block, based oninformation indicating whether inverse orthogonal transform has beenperformed on the current block and whether inverse secondary transformhas been performed on the plurality of transform coefficients of thecurrent block.

In this way, the decoder is capable of appropriately determining whetherto use the quantization matrix for the current block in the inversequantization processing, and thus is capable of increasing theprocessing efficiency while reducing decrease in subjective imagequality.

For example, when the current block is a rectangular block, thecircuitry may: generate a second quantization matrix for the pluralityof transform coefficients of the rectangular block by converting a firstquantization matrix for a plurality of transform coefficients of asquare block; and perform quantization on the plurality of transformcoefficient of the rectangular block, using the second quantizationmatrix.

In this way, the decoder is capable of generating the quantizationmatrix corresponding to the rectangular block based on the quantizationmatrix corresponding to the square block, and thus there is no need forthe decoder to decode a quantization matrix corresponding to therectangular block. Furthermore, the decoder is capable of using theappropriate quantization matrix also for the rectangular block withoutincreasing the processing amount. Accordingly, the decoder is capable ofefficiently quantizing rectangular blocks which have various shapes, andthus is capable of increasing the processing efficiency.

Furthermore, an encoding method according to an aspect of the presentdisclosure includes: performing quantization on a plurality of transformcoefficients of a current block to be encoded, using a quantizationmatrix when orthogonal transform is performed on the current block andsecondary transform is not performed on the current block; andperforming quantization on the plurality of transform coefficients ofthe current block without using the quantization matrix when orthogonaltransform is not performed on the current block and when both orthogonaltransform and secondary transform are performed on the current block.

In this way, an apparatus which executes the encoding method performsquantization, without using the quantization matrix, on the currentblock for which a sufficient effect of adjusting a subjective imagequality may not be obtained even if the quantization matrix is applied,which reduces the processing amount. Furthermore, the apparatus whichexecutes the encoding method is capable of appropriately applying thequantization matrix to a plurality of prediction residuals of theorthogonal-transformed current block, which provides an effect ofadjusting the subjective image quality. Accordingly, the apparatus whichexecutes the encoding method is capable of increasing the codingefficiency while reducing decrease in subjective image quality, both inthe case in which the quantization matrix is applied and in the case inwhich the quantization matrix is not applied.

Furthermore, a decoding method according to an aspect of the presentdisclosure includes: performing inverse quantization on a plurality oftransform coefficients of a current block to be decoded, using aquantization matrix when inverse orthogonal transform is performed onthe current block and inverse secondary transform is not performed onthe current block; and performing inverse quantization on the pluralityof transform coefficients of the current block without using thequantization matrix when inverse orthogonal transform is not performedon the current block and when both inverse orthogonal transform andinverse secondary transform are performed on the current block.

In this way, the apparatus which executes the decoding method performsinverse quantization, without using the quantization matrix, on thecurrent block for which a sufficient effect of adjusting a subjectiveimage quality may not be obtained even if the quantization matrix isapplied, which reduces the processing amount. Furthermore, the apparatuswhich executes the decoding method is capable of appropriately applyingthe quantization matrix for the current block on which orthogonaltransform, quantization, and encoding have been performed, whichprovides an effect of adjusting the subjective image quality.Accordingly, the apparatus which executes the decoding method is capableof increasing the processing efficiency while reducing decrease insubjective image quality, both in the case in which the quantizationmatrix is applied and in the case in which the quantization matrix isnot applied.

These general and specific aspects may be implemented using a system, adevice, a method, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, devices, methods, integrated circuits, computer programs, orcomputer-readable recording media.

Hereinafter, embodiments will be described with reference to thedrawings. Note that the embodiments described below each show a generalor specific example. The numerical values, shapes, materials,components, the arrangement and connection of the components, steps, therelation and order of the steps, etc., indicated in the followingembodiments are mere examples, and are not intended to limit the scopeof the claims.

Embodiments of an encoder and a decoder will be described below. Theembodiments are examples of an encoder and a decoder to which theprocesses and/or configurations presented in the description of aspectsof the present disclosure are applicable. The processes and/orconfigurations can also be implemented in an encoder and a decoderdifferent from those according to the embodiments. For example,regarding the processes and/or configurations as applied to theembodiments, any of the following may be implemented:

Any of the components of the encoder or the decoder according to theembodiments presented in the description of aspects of the presentdisclosure may be substituted or combined with another componentpresented anywhere in the description of aspects of the presentdisclosure.

In the encoder or the decoder according to the embodiments,discretionary changes may be made to functions or processes performed byone or more components of the encoder or the decoder, such as addition,substitution, removal, etc., of the functions or processes. For example,any function or process may be substituted or combined with anotherfunction or process presented anywhere in the description of aspects ofthe present disclosure.

In methods implemented by the encoder or the decoder according to theembodiments, discretionary changes may be made such as addition,substitution, and removal of one or more of the processes included inthe method. For example, any process in the method may be substituted orcombined with another process presented anywhere in the description ofaspects of the present disclosure.

One or more components included in the encoder or the decoder accordingto embodiments may be combined with a component presented anywhere inthe description of aspects of the present disclosure, may be combinedwith a component including one or more functions presented anywhere inthe description of aspects of the present disclosure, and may becombined with a component that implements one or more processesimplemented by a component presented in the description of aspects ofthe present disclosure.

A component including one or more functions of the encoder or thedecoder according to the embodiments, or a component that implements oneor more processes of the encoder or the decoder according to theembodiments, may be combined or substituted with a component presentedanywhere in the description of aspects of the present disclosure, with acomponent including one or more functions presented anywhere in thedescription of aspects of the present disclosure, or with a componentthat implements one or more processes presented anywhere in thedescription of aspects of the present disclosure.

In methods implemented by the encoder or the decoder according to theembodiments, any of the processes included in the method may besubstituted or combined with a process presented anywhere in thedescription of aspects of the present disclosure or with anycorresponding or equivalent process.

One or more processes included in methods implemented by the encoder orthe decoder according to the embodiments may be combined with a processpresented anywhere in the description of aspects of the presentdisclosure.

The implementation of the processes and/or configurations presented inthe description of aspects of the present disclosure is not limited tothe encoder or the decoder according to the embodiments. For example,the processes and/or configurations may be implemented in a device usedfor a purpose different from the moving picture encoder or the movingpicture decoder disclosed in the embodiments.

Encoder

First, an encoder according to an embodiment will be described. FIG. 1is a block diagram illustrating a configuration of encoder 100 accordingto the embodiment. Encoder 100 is a video encoder which encodes a videoin units of a block.

As illustrated in FIG. 1 , encoder 100 is an apparatus which encodes animage in units of a block, and includes splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, block memory 118, loop filter120, frame memory 122, intra predictor 124, inter predictor 126, andprediction controller 128.

Encoder 100 is implemented as, for example, a generic processor andmemory. In this case, when a software program stored in the memory isexecuted by the processor, the processor functions as splitter 102,subtractor 104, transformer 106, quantizer 108, entropy encoder 110,inverse quantizer 112, inverse transformer 114, adder 116, loop filter120, intra predictor 124, inter predictor 126, and prediction controller128. Alternatively, encoder 100 may be implemented as one or morededicated electronic circuits corresponding to splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, an overall flow of processes performed by encoder 100 isdescribed, and then each of constituent elements included in encoder 100will be described.

Overall Flow of Encoding Process

FIG. 2 is a flow chart indicating one example of an overall encodingprocess performed by encoder 100.

First, splitter 102 of encoder 100 splits each of pictures included inan input image which is a video into a plurality of blocks having afixed size (e.g., 128×128 pixels) (Step Sa_1). Splitter 102 then selectsa splitting pattern for the fixed-size block (also referred to as ablock shape) (Step Sa_2). In other words, splitter 102 further splitsthe fixed-size block into a plurality of blocks which form the selectedsplitting pattern. Encoder 100 performs, for each of the plurality ofblocks, Steps Sa_3 to Sa_9 for the block (that is a current block to beencoded).

In other words, a prediction processor which includes all or part ofintra predictor 124, inter predictor 126, and prediction controller 128generates a prediction signal (also referred to as a prediction block)of the current block to be encoded (also referred to as a current block)(Step Sa_3).

Next, subtractor 104 generates a difference between the current blockand a prediction block as a prediction residual (also referred to as adifference block) (Step Sa_4).

Next, transformer 106 transforms the difference block and quantizer 108quantizes the result, to generate a plurality of quantized coefficients(Step Sa_5). It is to be noted that the block having the plurality ofquantized coefficients is also referred to as a coefficient block.

Next, entropy encoder 110 encodes (specifically, entropy encodes) thecoefficient block and a prediction parameter related to generation of aprediction signal to generate an encoded signal (Step Sa_6). It is to benoted that the encoded signal is also referred to as an encodedbitstream, a compressed bitstream, or a stream.

Next, inverse quantizer 112 performs inverse quantization of thecoefficient block and inverse transformer 114 performs inverse transformof the result, to restore a plurality of prediction residuals (that is,a difference block) (Step Sa_7).

Next, adder 116 adds the prediction block to the restored differenceblock to reconstruct the current block as a reconstructed image (alsoreferred to as a reconstructed block or a decoded image block) (StepSa_8). In this way, the reconstructed image is generated.

When the reconstructed image is generated, loop filter 120 performsfiltering of the reconstructed image as necessary (Step Sa_9).

Encoder 100 then determines whether encoding of the entire picture hasbeen finished (Step Sa_10). When determining that the encoding has notyet been finished (No in Step Sa_10), processes from Step Sa_2 areexecuted repeatedly.

Although encoder 100 selects one splitting pattern for a fixed-sizeblock, and encodes each block according to the splitting pattern in theabove-described example, it is to be noted that each block may beencoded according to a corresponding one of a plurality of splittingpatterns. In this case, encoder 100 may evaluate a cost for each of theplurality of splitting patterns, and, for example, may select theencoded signal obtainable by encoding according to the splitting patternwhich yields the smallest cost as an encoded signal which is output.

As illustrated, the processes in Steps Sa_1 to Sa_10 are performedsequentially by encoder 100. Alternatively, two or more of the processesmay be performed in parallel, the processes may be reordered, etc.

Splitter

Splitter 102 splits each of pictures included in an input video into aplurality of blocks, and outputs each block to subtractor 104. Forexample, splitter 102 first splits a picture into blocks of a fixed size(for example, 128×128). Other fixed block sizes may be employed. Thefixed-size block is also referred to as a coding tree unit (CTU).Splitter 102 then splits each fixed-size block into blocks of variablesizes (for example, 64×64 or smaller), based on recursive quadtreeand/or binary tree block splitting. In other words, splitter 102 selectsa splitting pattern. The variable-size block is also referred to as acoding unit (CU), a prediction unit (PU), or a transform unit (TU). Itis to be noted that, in various kinds of processing examples, there isno need to differentiate between CU, PU, and TU; all or some of theblocks in a picture may be processed in units of a CU, a PU, or a TU.

FIG. 3 is a conceptual diagram illustrating one example of blocksplitting according to an embodiment. In FIG. 3 , the solid linesrepresent block boundaries of blocks split by quadtree block splitting,and the dashed lines represent block boundaries of blocks split bybinary tree block splitting.

Here, block 10 is a square block having 128×128 pixels (128×128 block).This 128×128 block 10 is first split into four square 64×64 blocks(quadtree block splitting).

The upper-left 64×64 block is further vertically split into tworectangular 32×64 blocks, and the left 32×64 block is further verticallysplit into two rectangular 16×64 blocks (binary tree block splitting).As a result, the upper-left 64×64 block is split into two 16×64 blocks11 and 12 and one 32×64 block 13.

The upper-right 64×64 block is horizontally split into two rectangular64×32 blocks 14 and 15 (binary tree block splitting).

The lower-left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The upper-left block and the lower-rightblock among the four 32×32 blocks are further split. The upper-left32×32 block is vertically split into two rectangle 16×32 blocks, and theright 16×32 block is further horizontally split into two 16×16 blocks(binary tree block splitting). The lower-right 32×32 block ishorizontally split into two 32×16 blocks (binary tree block splitting).As a result, the lower-left 64×64 block is split into 16×32 block 16,two 16×16 blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16blocks 21 and 22.

The lower-right 64×64 block 23 is not split.

As described above, in FIG. 3 , block 10 is split into thirteenvariable-size blocks 11 through 23 based on recursive quadtree andbinary tree block splitting. This type of splitting is also referred toas quadtree plus binary tree (QTBT) splitting.

It is to be noted that, in FIG. 3 , one block is split into four or twoblocks (quadtree or binary tree block splitting), but splitting is notlimited to these examples. For example, one block may be split intothree blocks (ternary block splitting). Splitting including such ternaryblock splitting is also referred to as multi-type tree (MBT) splitting.

Picture Structure: Slice/Tile

A picture may be configured in units of one or more slices or tiles inorder to decode the picture in parallel. The picture configured in unitsof one or more slices or tiles may be configured by splitter 102.

Slices are basic encoding units included in a picture. A picture mayinclude, for example, one or more slices. In addition, a slice includesone or more successive coding tree units (CTU).

FIG. 4A is a conceptual diagram illustrating one example of a sliceconfiguration. For example, a picture includes 11×8 CTUs and is splitinto four slices (slices 1 to 4). Slice 1 includes sixteen CTUs, slice 2includes twenty-one CTUs, slice 3 includes twenty-nine CTUs, and slice 4includes twenty-two CTUs. Here, each CTU in the picture belongs to oneof the slices. The shape of each slice is a shape obtainable bysplitting the picture horizontally. A boundary of each slice does notneed to be coincide with an image end, and may be coincide with any ofthe boundaries between CTUs in the image. The processing order of theCTUs in a slice (an encoding order or a decoding order) is, for example,a raster-scan order. A slice includes header information and encodeddata. Features of the slice may be described in header information. Thefeatures include a CTU address of a top CTU in the slice, a slice type,etc.

A tile is a unit of a rectangular region included in a picture. Each oftiles may be assigned with a number referred to as TileId in raster-scanorder.

FIG. 4B is a conceptual diagram indicating an example of a tileconfiguration. For example, a picture includes 11×8 CTUs and is splitinto four tiles of rectangular regions (tiles 1 to 4). When tiles areused, the processing order of CTUs are changed from the processing orderin the case where no tile is used. When no tile is used, CTUs in apicture are processed in raster-scan order. When tiles are used, atleast one CTU in each of the tiles is processed in raster-scan order.For example, as illustrated in FIG. 4B, the processing order of the CTUsincluded in tile 1 is the order which starts from the left-end of thefirst row of tile 1 toward the right-end of the first row of tile 1 andthen starts from the left-end of the second row of tile 1 toward theright-end of the second row of tile 1.

It is to be noted that the one tile may include one or more slices, andone slice may include one or more tiles.

Subtractor

Subtractor 104 subtracts a prediction signal (prediction sample that isinput from prediction controller 128 indicated below) from an originalsignal (original sample) in units of a block input from splitter 102 andsplit by splitter 102. In other words, subtractor 104 calculatesprediction errors (also referred to as residuals) of a block to beencoded (hereinafter also referred to as a current block). Subtractor104 then outputs the calculated prediction errors (residuals) totransformer 106.

The original signal is a signal which has been input into encoder 100and represents an image of each picture included in a video (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

Transformer

Transformer 106 transforms prediction errors in spatial domain intotransform coefficients in frequency domain, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a defined discrete cosine transform (DCT) ordiscrete sine transform (DST) to prediction errors in spatial domain.The defined DCT or DST may be predefined.

It is to be noted that transformer 106 may adaptively select a transformtype from among a plurality of transform types, and transform predictionerrors into transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 5A is a chart indicating transform basisfunctions for the example transform types. In FIG. 5A, N indicates thenumber of input pixels. For example, selection of a transform type fromamong the plurality of transform types may depend on a prediction type(one of intra prediction and inter prediction), and may depend on anintra prediction mode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an EMT flag or an AMT flag) and information indicating theselected transform type is normally signaled at the CU level. It is tobe noted that the signaling of such information does not necessarilyneed to be performed at the CU level, and may be performed at anotherlevel (for example, at the bit sequence level, picture level, slicelevel, tile level, or CTU level).

In addition, transformer 106 may re-transform the transform coefficients(transform result). Such re-transform is also referred to as adaptivesecondary transform (AST) or non-separable secondary transform (NSST).For example, transformer 106 performs re-transform in units of asub-block (for example, 4×4 sub-block) included in a transformcoefficient block corresponding to an intra prediction error.Information indicating whether to apply NSST and information related toa transform matrix for use in NSST are normally signaled at the CUlevel. It is to be noted that the signaling of such information does notnecessarily need to be performed at the CU level, and may be performedat another level (for example, at the sequence level, picture level,slice level, tile level, or CTU level).

Transformer 106 may employ a separable transform and a non-separabletransform. A separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach of a number of directions according to the number of dimensions ofinputs. A non-separable transform is a method of performing a collectivetransform in which two or more dimensions in multidimensional inputs arecollectively regarded as a single dimension.

In one example of a non-separable transform, when an input is a 4×4block, the 4×4 block is regarded as a single array including sixteenelements, and the transform applies a 16×16 transform matrix to thearray.

In another example of a non-separable transform, a 4×4 input block isregarded as a single array including sixteen elements, and then atransform (hypercube givens transform) in which givens revolution isperformed on the array a plurality of times may be performed.

In the transform in transformer 106, the types of bases to betransformed into the frequency domain according to regions in a CU canbe switched. Examples include spatially varying transforms (SVT). InSVT, as illustrated in FIG. 5B, CUs are split into two equal regionshorizontally or vertically, and only one of the regions is transformedinto the frequency domain. A transform basis type can be set for eachregion. For example, DST7 and DST8 are used. In this example, only oneof these two regions in the CU is transformed, and the other is nottransformed. However, both of these two regions may be transformed. Inaddition, the splitting method is not limited to the splitting into twoequal regions, and can be more flexible. For example, the CU may besplit into four equal regions, or information indicating splitting maybe encoded separately and be signaled in the same manner as the CUsplitting. It is to be noted that SVT is also referred to as sub-blocktransform (SBT).

Quantizer

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in a determinedscanning order, the transform coefficients of the current block, andquantizes the scanned transform coefficients based on quantizationparameters (QP) corresponding to the transform coefficients. Quantizer108 then outputs the quantized transform coefficients (hereinafter alsoreferred to as quantized coefficients) of the current block to entropyencoder 110 and inverse quantizer 112. The determined scanning order maybe predetermined.

A determined scanning order is an order for quantizing/inversequantizing transform coefficients. For example, a determined scanningorder may be defined as ascending order of frequency (from low to highfrequency) or descending order of frequency (from high to lowfrequency).

A quantization parameter (QP) is a parameter defining a quantizationstep (quantization width). For example, when the value of thequantization parameter increases, the quantization step also increases.In other words, when the value of the quantization parameter increases,the quantization error increases.

In addition, a quantization matrix may be used for quantization. Forexample, several kinds of quantization matrices may be usedcorrespondingly to frequency transform sizes such as 4×4 and 8×8,prediction modes such as intra prediction and inter prediction, andpixel components such as luma and chroma pixel components. It is to benoted that quantization means digitalizing values sampled at determinedintervals correspondingly to determined levels. In this technical field,quantization may be referred to using other expressions, such asrounding and scaling, and may employ rounding and scaling. Thedetermined intervals and levels may be predetermined.

Methods using quantization matrices include a method using aquantization matrix which has been set directly at the encoder side anda method using a quantization matrix which has been set as a default(default matrix). At the encoder side, a quantization matrix suitablefor features of an image can be set by directly setting a quantizationmatrix. This case, however, has a disadvantage of increasing a codingamount for encoding the quantization matrix.

There is a method for quantizing a high-frequency coefficient and alow-frequency coefficient without using a quantization matrix. It is tobe noted that this method is equivalent to a method using a quantizationmatrix (flat matrix) whose coefficients have the same value.

The quantization matrix may be specified using, for example, a sequenceparameter set (SPS) or a picture parameter set (PPS). The SPS includes aparameter which is used for a sequence, and the PPS includes a parameterwhich is used for a picture. Each of the SPS and the PPS may be simplyreferred to as a parameter set.

Entropy Encoder

Entropy encoder 110 generates an encoded signal (encoded bitstream)based on quantized coefficients which have been input from quantizer108. More specifically, entropy encoder 110, for example, binarizesquantized coefficients, and arithmetically encodes the binary signal,and outputs a compressed bit stream or sequence.

Inverse Quantizer

Inverse quantizer 112 inverse quantizes quantized coefficients whichhave been input from quantizer 108. More specifically, inverse quantizer112 inverse quantizes, in a determined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114. The determined scanning order may bepredetermined.

Inverse Transformer

Inverse transformer 114 restores prediction errors (residuals) byinverse transforming transform coefficients which have been input frominverse quantizer 112. More specifically, inverse transformer 114restores the prediction errors of the current block by applying aninverse transform corresponding to the transform applied by transformer106 on the transform coefficients. Inverse transformer 114 then outputsthe restored prediction errors to adder 116.

It is to be noted that since information is lost in quantization, therestored prediction errors do not match the prediction errors calculatedby subtractor 104. In other words, the restored prediction errorsnormally include quantization errors.

Adder

Adder 116 reconstructs the current block by adding prediction errorswhich have been input from inverse transformer 114 and predictionsamples which have been input from prediction controller 128. Adder 116then outputs the reconstructed block to block memory 118 and loop filter120. A reconstructed block is also referred to as a local decoded block.

Block Memory

Block memory 118 is, for example, storage for storing blocks in apicture to be encoded (hereinafter referred to as a current picture)which is referred to in intra prediction. More specifically, blockmemory 118 stores reconstructed blocks output from adder 116.

Frame Memory

Frame memory 122 is, for example, storage for storing reference picturesfor use in inter prediction, and is also referred to as a frame buffer.More specifically, frame memory 122 stores reconstructed blocks filteredby loop filter 120.

Loop Filter

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF or DBF), a sampleadaptive offset (SAO), and an adaptive loop filter (ALF).

In an ALF, a least square error filter for removing compressionartifacts is applied. For example, one filter selected from among aplurality of filters based on the direction and activity of localgradients is applied for each of 2×2 sub-blocks in the current block.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, fifteen or twenty-five classes). The classification of thesub-block is based on gradient directionality and activity. For example,classification index C (for example, C = 5D + A) is derived based ongradient directionality D (for example, 0 to 2 or 0 to 4) and gradientactivity A (for example, 0 to 4). Then, based on classification index C,each sub-block is categorized into one out of a plurality of classes.

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by adding gradients of a plurality ofdirections and quantizing the result of addition.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in an ALF is, for example, a circularsymmetric filter shape. FIG. 6A through FIG. 6C illustrate examples offilter shapes used in ALFs. FIG. 6A illustrates a 5×5 diamond shapefilter, FIG. 6B illustrates a 7×7 diamond shape filter, and FIG. 6Cillustrates a 9×9 diamond shape filter. Information indicating thefilter shape is normally signaled at the picture level. It is to benoted that the signaling of such information indicating the filter shapedoes not necessarily need to be performed at the picture level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, CTU level, or CU level).

The ON or OFF of the ALF is determined, for example, at the picturelevel or CU level. For example, the decision of whether to apply the ALFto luma may be made at the CU level, and the decision of whether toapply ALF to chroma may be made at the picture level. Informationindicating ON or OFF of the ALF is normally signaled at the picturelevel or CU level. It is to be noted that the signaling of informationindicating ON or OFF of the ALF does not necessarily need to beperformed at the picture level or CU level, and may be performed atanother level (for example, at the sequence level, slice level, tilelevel, or CTU level).

The coefficient set for the plurality of selectable filters (forexample, fifteen or up to twenty-five filters) is normally signaled atthe picture level. It is to be noted that the signaling of thecoefficient set does not necessarily need to be performed at the picturelevel, and may be performed at another level (for example, at thesequence level, slice level, tile level, CTU level, CU level, orsub-block level).

Loop Filter > Deblocking Filter

In a deblocking filter, loop filter 120 performs a filter process on ablock boundary in a reconstructed image so as to reduce distortion whichoccurs at the block boundary.

FIG. 7 is a block diagram illustrating one example of a specificconfiguration of loop filter 120 which functions as a deblocking filter.

Loop filter 120 includes: boundary determiner 1201; filter determiner1203; filtering executor 1205; process determiner 1208; filtercharacteristic determiner 1207; and switches 1202, 1204, and 1206.

Boundary determiner 1201 determines whether a pixel to bedeblock-filtered (that is, a current pixel) is present around a blockboundary. Boundary determiner 1201 then outputs the determination resultto switch 1202 and processing determiner 1208.

In the case where boundary determiner 1201 has determined that a currentpixel is present around a block boundary, switch 1202 outputs anunfiltered image to switch 1204. In the opposite case where boundarydeterminer 1201 has determined that no current pixel is present around ablock boundary, switch 1202 outputs an unfiltered image to switch 1206.

Filter determiner 1203 determines whether to perform deblockingfiltering of the current pixel, based on the pixel value of at least onesurrounding pixel located around the current pixel. Filter determiner1203 then outputs the determination result to switch 1204 and processingdeterminer 1208.

In the case where filter determiner 1203 has determined to performdeblocking filtering of the current pixel, switch 1204 outputs theunfiltered image obtained through switch 1202 to filtering executor1205. In the opposite case were filter determiner 1203 has determinednot to perform deblocking filtering of the current pixel, switch 1204outputs the unfiltered image obtained through switch 1202 to switch1206.

When obtaining the unfiltered image through switches 1202 and 1204,filtering executor 1205 executes, for the current pixel, deblockingfiltering with the filter characteristic determined by filtercharacteristic determiner 1207. Filtering executor 1205 then outputs thefiltered pixel to switch 1206.

Under control by processing determiner 1208, switch 1206 selectivelyoutputs a pixel which has not been deblock-filtered and a pixel whichhas been deblock-filtered by filtering executor 1205.

Processing determiner 1208 controls switch 1206 based on the results ofdeterminations made by boundary determiner 1201 and filter determiner1203. In other words, processing determiner 1208 causes switch 1206 tooutput the pixel which has been deblock-filtered when boundarydeterminer 1201 has determined that the current pixel is present aroundthe block boundary and filter determiner 1203 has determined to performdeblocking filtering of the current pixel. In addition, other than theabove case, processing determiner 1208 causes switch 1206 to output thepixel which has not been deblock-filtered. A filtered image is outputfrom switch 1206 by repeating output of a pixel in this way.

FIG. 8 is a conceptual diagram indicating an example of a deblockingfilter having a symmetrical filtering characteristic with respect to ablock boundary.

In a deblocking filter process, one of two deblocking filters havingdifferent characteristics, that is, a strong filter and a weak filter isselected using pixel values and quantization parameters. In the case ofthe strong filter, pixels p0 to p2 and pixels q0 to q2 are presentacross a block boundary as illustrated in FIG. 8 , the pixel values ofthe respective pixel q0 to q2 are changed to pixel values q′0 to q′2 byperforming, for example, computations according to the expressionsbelow.

q′0 = (p1 + 2 × p0 + 2 × q0 + 2×q1 + q2 + 4)/8

q′1 = (p0 + q0 + q1 + q2 + 2)/4

q′2 = (p0 + q0 + q1 + 3 × q2 + 2 × q3 + 4)/8

It is to be noted that, in the above expressions, p0 to p2 and q0 to q2are the pixel values of respective pixels p0 to p2 and pixels q0 to q2.In addition, q3 is the pixel value of neighboring pixel q3 located atthe opposite side of pixel q2 with respect to the block boundary. Inaddition, in the right side of each of the expressions, coefficientswhich are multiplied with the respective pixel values of the pixels tobe used for deblocking filtering are filter coefficients.

Furthermore, in the deblocking filtering, clipping may be performed sothat the calculated pixel values are not set over a threshold value. Inthe clipping process, the pixel values calculated according to the aboveexpressions are clipped to a value obtained according to “a computationpixel value ± 2 × a threshold value” using the threshold valuedetermined based on a quantization parameter. In this way, it ispossible to prevent excessive smoothing.

FIG. 9 is a conceptual diagram for illustrating a block boundary onwhich a deblocking filter process is performed. FIG. 10 is a conceptualdiagram indicating examples of Bs values.

The block boundary on which the deblocking filter process is performedis, for example, a boundary between prediction units (PU) having 8×8pixel blocks as illustrated in FIG. 9 or a boundary between transformunits (TU). The deblocking filter process may be performed in units offour rows or four columns. First, boundary strength (Bs) values aredetermined as indicated in FIG. 10 for block P and block Q illustratedin FIG. 9 .

According to the Bs values in FIG. 10 , whether to perform deblockingfilter processes of block boundaries belonging to the same image usingdifferent strengths is determined. The deblocking filter process for achroma signal is performed when a Bs value is 2. The deblocking filterprocess for a luma signal is performed when a Bs value is 1 or more anda determined condition is satisfied. The determined condition may bepredetermined. It is to be noted that conditions for determining Bsvalues are not limited to those indicated in FIG. 10 , and a Bs valuemay be determined based on another parameter.

Prediction Processor (Intra Predictor, Inter Predictor, PredictionController)

FIG. 11 is a flow chart illustrating one example of a process performedby the prediction processor of encoder 100. It is to be noted that theprediction processor includes all or part of the following constituentelements: intra predictor 124; inter predictor 126; and predictioncontroller 128.

The prediction processor generates a prediction image of a current block(Step Sb_1). This prediction image is also referred to as a predictionsignal or a prediction block. It is to be noted that the predictionsignal is, for example, an intra prediction signal or an interprediction signal. Specifically, the prediction processor generates theprediction image of the current block using a reconstructed image whichhas been already obtained through generation of a prediction block,generation of a difference block, generation of a coefficient block,restoring of a difference block, and generation of a decoded imageblock.

The reconstructed image may be, for example, an image in a referencepicture, or an image of an encoded block in a current picture which isthe picture including the current block. The encoded block in thecurrent picture is, for example, a neighboring block of the currentblock.

FIG. 12 is a flow chart illustrating another example of a processperformed by the prediction processor of encoder 100.

The prediction processor generates a prediction image using a firstmethod (Step Sc_1 a), generates a prediction image using a second method(Step Sc_1 b), and generates a prediction image using a third method(Step Sc_1 c). The first method, the second method, and the third methodmay be mutually different methods for generating a prediction image.Each of the first to third methods may be an inter prediction method, anintra prediction method, or another prediction method. Theabove-described reconstructed image may be used in these predictionmethods.

Next, the prediction processor selects any one of a plurality ofprediction methods generated in Steps Sc_1 a, Sc_1 b, and Sc_1c (StepSc_2). The selection of the prediction image, that is selection of amethod or a mode for obtaining a final prediction image may be made bycalculating a cost for each of the generated prediction images and basedon the cost. Alternatively, the selection of the prediction image may bemade based on a parameter which is used in an encoding process. Encoder100 may transform information for identifying a selected predictionimage, a method, or a mode into an encoded signal (also referred to asan encoded bitstream). The information may be, for example, a flag orthe like. In this way, the decoder is capable of generating a predictionimage according to the method or the mode selected based on theinformation in encoder 100. It is to be noted that, in the exampleillustrated in FIG. 12 , the prediction processor selects any of theprediction images after the prediction images are generated using therespective methods. However, the prediction processor may select amethod or a mode based on a parameter for use in the above-describedencoding process before generating prediction images, and may generate aprediction image according to the method or mode selected.

For example, the first method and the second method may be intraprediction and inter prediction, respectively, and the predictionprocessor may select a final prediction image for a current block fromprediction images generated according to the prediction methods.

FIG. 13 is a flow chart illustrating another example of a processperformed by the prediction processor of encoder 100.

First, the prediction processor generates a prediction image using intraprediction (Step Sd_1 a), and generates a prediction image using interprediction (Step Sd_1 b). It is to be noted that the prediction imagegenerated by intra prediction is also referred to as an intra predictionimage, and the prediction image generated by inter prediction is alsoreferred to as an inter prediction image.

Next, the prediction processor evaluates each of the intra predictionimage and the inter prediction image (Step Sd_2). A cost may be used inthe evaluation. In other words, the prediction processor calculates costC for each of the intra prediction image and the inter prediction image.Cost C may be calculated according to an expression of an R-Doptimization model, for example, C =D + λ × R. In this expression, Dindicates a coding distortion of a prediction image, and is representedas, for example, a sum of absolute differences between the pixel valueof a current block and the pixel value of a prediction image. Inaddition, R indicates a predicted coding amount of a prediction image,specifically, the coding amount required to encode motion informationfor generating a prediction image, etc. In addition, λ indicates, forexample, a multiplier according to the method of Lagrange multiplier.

The prediction processor then selects the prediction image for which thesmallest cost C has been calculated among the intra prediction image andthe inter prediction image, as the final prediction image for thecurrent block (Step Sd_3). In other words, the prediction method or themode for generating the prediction image for the current block isselected.

Intra Predictor

Intra predictor 124 generates a prediction signal (intra predictionsignal) by performing intra prediction (also referred to as intra frameprediction) of the current block by referring to a block or blocks inthe current picture and stored in block memory 118. More specifically,intra predictor 124 generates an intra prediction signal by performingintra prediction by referring to samples (for example, luma and/orchroma values) of a block or blocks neighboring the current block, andthen outputs the intra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of intra prediction modes which have beendefined. The intra prediction modes include one or more non-directionalprediction modes and a plurality of directional prediction modes. Thedefined modes may be predefined.

The one or more non-directional prediction modes include, for example,the planar prediction mode and DC prediction mode defined in the H.265 /high-efficiency video coding (HEVC) standard.

The plurality of directional prediction modes include, for example, thethirty-three directional prediction modes defined in the H.265/HEVCstandard. It is to be noted that the plurality of directional predictionmodes may further include thirty-two directional prediction modes inaddition to the thirty-three directional prediction modes (for a totalof sixty-five directional prediction modes). FIG. 14 is a conceptualdiagram illustrating sixty-seven intra prediction modes in total thatmay be used in intra prediction (two non-directional prediction modesand sixty-five directional prediction modes). The solid arrows representthe thirty-three directions defined in the H.265/HEVC standard, and thedashed arrows represent the additional thirty-two directions (the twonon-directional prediction modes are not illustrated in FIG. 14 ).

In various kinds of processing examples, a luma block may be referred toin intra prediction of a chroma block. In other words, a chromacomponent of the current block may be predicted based on a lumacomponent of the current block. Such intra prediction is also referredto as cross-component linear model (CCLM) prediction. The intraprediction mode for a chroma block in which such a luma block isreferred to (also referred to as, for example, a CCLM mode) may be addedas one of the intra prediction modes for chroma blocks.

Intra predictor 124 may correct intra-predicted pixel values based onhorizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC (referred to as, for example, a PDPC flag) isnormally signaled at the CU level. It is to be noted that the signalingof such information does not necessarily need to be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, or CTU level).

Inter Predictor

Inter predictor 126 generates a prediction signal (inter predictionsignal) by performing inter prediction (also referred to as inter frameprediction) of the current block by referring to a block or blocks in areference picture, which is different from the current picture and isstored in frame memory 122. Inter prediction is performed in units of acurrent block or a current sub-block (for example, a 4×4 block) in thecurrent block. For example, inter predictor 126 performs motionestimation in a reference picture for the current block or the currentsub-block, and finds out a reference block or a sub-block which bestmatches the current block or the current sub-block. Inter predictor 126then obtains motion information (for example, a motion vector) whichcompensates a motion or a change from the reference block or thesub-block to the current block or the sub-block. Inter predictor 126generates an inter prediction signal of the current block or thesub-block by performing motion compensation (or motion prediction) basedon the motion information. Inter predictor 126 outputs the generatedinter prediction signal to prediction controller 128.

The motion information used in motion compensation may be signaled asinter prediction signals in various forms. For example, a motion vectormay be signaled. As another example, the difference between a motionvector and a motion vector predictor may be signaled.

Basic Flow of Inter Prediction

FIG. 15 is a flow chart illustrating an example basic processing flow ofinter prediction.

First, inter predictor 126 generates a prediction signal (Steps Se_1 toSe_3). Next, subtractor 104 generates the difference between a currentblock and a prediction image as a prediction residual (Step Se_4).

Here, in the generation of the prediction image, inter predictor 126generates the prediction image through determination of a motion vector(MV) of the current block (Steps Se_1 and Se_2) and motion compensation(Step Se_3). Furthermore, in determination of an MV, inter predictor 126determines the MV through selection of a motion vector candidate (MVcandidate) (Step Se_1) and derivation of an MV (Step Se_2). Theselection of the MV candidate is made by, for example, selecting atleast one MV candidate from an MV candidate list. Alternatively, inderivation of an MV, inter predictor 126 may further select at least oneMV candidate from the at least one MV candidate, and determine theselected at least one MV candidate as the MV for the current block.Alternatively, inter predictor 126 may determine the MV for the currentblock by performing estimation in a reference picture region specifiedby each of the selected at least one MV candidate. It is to be notedthat the estimation in a reference picture region may be referred to asmotion estimation.

In addition, although Steps Se_1 to Se_3 are performed by interpredictor 126 in the above-described example, a process that is forexample Step Se_1, Step Se_2, or the like may be performed by anotherconstituent element included in encoder 100.

Motion Vector Derivation Flow

FIG. 16 is a flow chart illustrating one example of derivation of motionvectors.

Inter predictor 126 derives an MV of a current block in a mode forencoding motion information (for example, an MV). In this case, forexample, the motion information is encoded as a prediction parameter,and is signaled. In other words, the encoded motion information isincluded in an encoded signal (also referred to as an encodedbitstream).

Alternatively, inter predictor 126 derives an MV in a mode in whichmotion information is not encoded. In this case, no motion informationis included in an encoded signal.

Here, MV derivation modes may include a normal inter mode, a merge mode,a FRUC mode, an affine mode, etc. which are described later. Modes inwhich motion information is encoded among the modes include the normalinter mode, the merge mode, the affine mode (specifically, an affineinter mode and an affine merge mode), etc. It is to be noted that motioninformation may include not only an MV but also motion vector predictorselection information which is described later. Modes in which no motioninformation is encoded include the FRUC mode, etc. Inter predictor 126selects a mode for deriving an MV of the current block from the modes,and derives the MV of the current block using the selected mode.

FIG. 17 is a flow chart illustrating another example of derivation ofmotion vectors.

Inter predictor 126 derives an MV of a current block in a mode in whichan MV difference is encoded. In this case, for example, the MVdifference is encoded as a prediction parameter, and is signaled. Inother words, the encoded MV difference is included in an encoded signal.The MV difference is the difference between the MV of the current blockand the MV predictor.

Alternatively, inter predictor 126 derives an MV in a mode in which noMV difference is encoded. In this case, no encoded MV difference isincluded in an encoded signal.

Here, as described above, the MV derivation modes include the normalinter mode, the merge mode, the FRUC mode, the affine mode, etc. whichare described later. Modes in which an MV difference is encoded amongthe modes include the normal inter mode, the affine mode (specifically,the affine inter mode), etc. Modes in which no MV difference is encodedinclude the FRUC mode, the merge mode, the affine mode (specifically,the affine merge mode), etc. Inter predictor 126 selects a mode forderiving an MV of the current block from the plurality of modes, andderives the MV of the current block using the selected mode.

Motion Vector Derivation Flow

FIG. 18 is a flow chart illustrating another example of derivation ofmotion vectors. The MV derivation modes which are inter prediction modesinclude a plurality of modes and are roughly divided into modes in whichan MV difference is encoded and modes in which no motion vectordifference is encoded. The modes in which no MV difference is encodedinclude the merge mode, the FRUC mode, the affine mode (specifically,the affine merge mode), etc. These modes are described in detail later.Simply, the merge mode is a mode for deriving an MV of a current blockby selecting a motion vector from an encoded surrounding block, and theFRUC mode is a mode for deriving an MV of a current block by performingestimation between encoded regions. The affine mode is a mode forderiving, as an MV of a current block, a motion vector of each of aplurality of sub-blocks included in the current block, assuming affinetransform.

More specifically, as illustrated when the inter prediction modeinformation indicates 0 (0 in Sf_1), inter predictor 126 derives amotion vector using the merge mode (Sf_2). When the inter predictionmode information indicates 1 (1 in Sf_1), inter predictor 126 derives amotion vector using the FRUC mode (Sf_3). When the inter prediction modeinformation indicates 2 (2 in Sf_1), inter predictor 126 derives amotion vector using the affine mode (specifically, the affine mergemode) (Sf_4). When the inter prediction mode information indicates 3 (3in Sf_1), inter predictor 126 derives a motion vector using a mode inwhich an MV difference is encoded (for example, a normal inter mode(Sf_5).

MV Derivation > Normal Inter Mode

The normal inter mode is an inter prediction mode for deriving an MV ofa current block based on a block similar to the image of the currentblock from a reference picture region specified by an MV candidate. Inthis normal inter mode, an MV difference is encoded.

FIG. 19 is a flow chart illustrating an example of inter prediction innormal inter mode.

First, inter predictor 126 obtains a plurality of MV candidates for acurrent block based on information such as MVs of a plurality of encodedblocks temporally or spatially surrounding the current block (StepSg_1). In other words, inter predictor 126 generates an MV candidatelist.

Next, inter predictor 126 extracts N (an integer of 2 or larger) MVcandidates from the plurality of MV candidates obtained in Step Sg_1, asmotion vector predictor candidates (also referred to as MV predictorcandidates) according to a determined priority order (Step Sg_2). It isto be noted that the priority order may be determined in advance foreach of the N MV candidates.

Next, inter predictor 126 selects one motion vector predictor candidatefrom the N motion vector predictor candidates, as the motion vectorpredictor (also referred to as an MV predictor) of the current block(Step Sg_3). At this time, inter predictor 126 encodes, in a stream,motion vector predictor selection information for identifying theselected motion vector predictor. It is to be noted that the stream isan encoded signal or an encoded bitstream as described above.

Next, inter predictor 126 derives an MV of a current block by referringto an encoded reference picture (Step Sg_4). At this time, interpredictor 126 further encodes, in the stream, the difference valuebetween the derived MV and the motion vector predictor as an MVdifference. It is to be noted that the encoded reference picture is apicture including a plurality of blocks which have been reconstructedafter being encoded.

Lastly, inter predictor 126 generates a prediction image for the currentblock by performing motion compensation of the current block using thederived MV and the encoded reference picture (Step Sg_5). It is to benoted that the prediction image is an inter prediction signal asdescribed above.

In addition, information indicating the inter prediction mode (normalinter mode in the above example) used to generate the prediction imageis, for example, encoded as a prediction parameter.

It is to be noted that the MV candidate list may be also used as a listfor use in another mode. In addition, the processes related to the MVcandidate list may be applied to processes related to the list for usein another mode. The processes related to the MV candidate list include,for example, extraction or selection of an MV candidate from the MVcandidate list, reordering of MV candidates, or deletion of an MVcandidate.

MV Derivation > Merge Mode

The merge mode is an inter prediction mode for selecting an MV candidatefrom an MV candidate list as an MV of a current block, thereby derivingthe MV.

FIG. 20 is a flow chart illustrating an example of inter prediction inmerge mode.

First, inter predictor 126 obtains a plurality of MV candidates for acurrent block based on information such as MVs of a plurality of encodedblocks temporally or spatially surrounding the current block (StepSh_1). In other words, inter predictor 126 generates an MV candidatelist.

Next, inter predictor 126 selects one MV candidate from the plurality ofMV candidates obtained in Step Sh_1, thereby deriving an MV of thecurrent block (Step Sh_2). At this time, inter predictor 126 encodes, ina stream, MV selection information for identifying the selected MVcandidate.

Lastly, inter predictor 126 generates a prediction image for the currentblock by performing motion compensation of the current block using thederived MV and the encoded reference picture (Step Sh_3).

In addition, information indicating the inter prediction mode (mergemode in the above example) used to generate the prediction image andincluded in the encoded signal is, for example, encoded as a predictionparameter.

FIG. 21 is a conceptual diagram for illustrating one example of a motionvector derivation process of a current picture in merge mode.

First, an MV candidate list in which MV predictor candidates areregistered is generated. Examples of MV predictor candidates include:spatially neighboring MV predictors which are MVs of a plurality ofencoded blocks located spatially surrounding a current block; temporallyneighboring MV predictors which are MVs of surrounding blocks on whichthe position of a current block in an encoded reference picture isprojected; combined MV predictors which are MVs generated by combiningthe MV value of a spatially neighboring MV predictor and the MV of atemporally neighboring MV predictor; and a zero MV predictor which is anMV having a zero value.

Next, one MV predictor is selected from a plurality of MV predictorsregistered in an MV predictor list, and the selected MV predictor isdetermined as the MV of a current block.

Furthermore, the variable length encoder describes and encodes, in astream, merge_idx which is a signal indicating which MV predictor hasbeen selected.

It is to be noted that the MV predictors registered in the MV predictorlist described in FIG. 21 are examples. The number of MV predictors maybe different from the number of MV predictors in the diagram, the MVpredictor list may be configured in such a manner that some of the kindsof the MV predictors in the diagram may not be included, or that one ormore MV predictors other than the kinds of MV predictors in the diagramare included.

A final MV may be determined by performing a decoder motion vectorrefinement process (DMVR) to be described later using the MV of thecurrent block derived in merge mode.

It is to be noted that the MV predictor candidates are MV candidatesdescribed above, and the MV predictor list is the MV candidate listdescribed above. It is to be noted that the MV candidate list may bereferred to as a candidate list. In addition, merge_idx is MV selectioninformation.

MV Derivation > FRUC Mode

Motion information may be derived at the decoder side without beingsignaled from the encoder side. It is to be noted that, as describedabove, the merge mode defined in the H.265/HEVC standard may be used. Inaddition, for example, motion information may be derived by performingmotion estimation at the decoder side. In an embodiment, at the decoderside, motion estimation is performed without using any pixel value in acurrent block.

Here, a mode for performing motion estimation at the decoder side isdescribed. The mode for performing motion estimation at the decoder sidemay be referred to as a pattern matched motion vector derivation (PMMVD)mode, or a frame rate up-conversion (FRUC) mode.

One example of a FRUC process in the form of a flow chart is illustratedin FIG. 22 . First, a list of a plurality of candidates each having amotion vector (MV) predictor (that is, an MV candidate list that may bealso used as a merge list) is generated by referring to a motion vectorin an encoded block which spatially or temporally neighbors a currentblock (Step Si_1). Next, a best MV candidate is selected from theplurality of MV candidates registered in the MV candidate list (StepSi_2). For example, the evaluation values of the respective MVcandidates included in the MV candidate list are calculated, and one MVcandidate is selected based on the evaluation values. Based on theselected motion vector candidates, a motion vector for the current blockis then derived (Step Si_4). More specifically, for example, theselected motion vector candidate (best MV candidate) is derived directlyas the motion vector for the current block. In addition, for example,the motion vector for the current block may be derived using patternmatching in a surrounding region of a position in a reference picturewhere the position in the reference picture corresponds to the selectedmotion vector candidate. In other words, estimation using the patternmatching and the evaluation values may be performed in the surroundingregion of the best MV candidate, and when there is an MV that yields abetter evaluation value, the best MV candidate may be updated to the MVthat yields the better evaluation value, and the updated MV may bedetermined as the final MV for the current block. A configuration inwhich no such a process for updating the best MV candidate to the MVhaving a better evaluation value is performed is also possible.

Lastly, inter predictor 126 generates a prediction image for the currentblock by performing motion compensation of the current block using thederived MV and the encoded reference picture (Step Si_5).

A similar process may be performed in units of a sub-block.

Evaluation values may be calculated according to various kinds ofmethods. For example, a comparison is made between a reconstructed imagein a region in a reference picture corresponding to a motion vector anda reconstructed image in a determined region (the region may be, forexample, a region in another reference picture or a region in aneighboring block of a current picture, as indicated below). Thedetermined region may be predetermined.

The difference between the pixel values of the two reconstructed imagesmay be used for an evaluation value of the motion vectors. It is to benoted that an evaluation value may be calculated using information otherthan the value of the difference.

Next, an example of pattern matching is described in detail. First, oneMV candidate included in an MV candidate list (for example, a mergelist) is selected as a start point of estimation by the patternmatching. For example, as the pattern matching, either a first patternmatching or a second pattern matching may be used. The first patternmatching and the second pattern matching are also referred to asbilateral matching and template matching, respectively.

MV Derivation > FRUC > Bilateral Matching

In the first pattern matching, pattern matching is performed between twoblocks along a motion trajectory of a current block which are two blocksin different two reference pictures. Accordingly, in the first patternmatching, a region in another reference picture along the motiontrajectory of the current block is used as a determined region forcalculating the evaluation value of the above-described candidate. Thedetermined region may be predetermined.

FIG. 23 is a conceptual diagram for illustrating one example of thefirst pattern matching (bilateral matching) between the two blocks inthe two reference pictures along the motion trajectory. As illustratedin FIG. 23 , in the first pattern matching, two motion vectors (MV0,MV1) are derived by estimating a pair which best matches among pairs inthe two blocks in the two different reference pictures (Ref0, Refl)which are the two blocks along the motion trajectory of the currentblock (Cur block). More specifically, a difference between thereconstructed image at a specified location in the first encodedreference picture (Ref0) specified by an MV candidate and thereconstructed image at a specified location in the second encodedreference picture (Ref1) specified by a symmetrical MV obtained byscaling the MV candidate at a display time interval is derived for thecurrent block, and an evaluation value is calculated using the value ofthe obtained difference. It is possible to select, as the final MV, theMV candidate which yields the best evaluation value among the pluralityof MV candidates, and which is likely to produce good results.

In the assumption of a continuous motion trajectory, the motion vectors(MVO, MV1) specifying the two reference blocks are proportional totemporal distances (TD0, TD1) between the current picture (Cur Pic) andthe two reference pictures (Ref0, Refl). For example, when the currentpicture is temporally located between the two reference pictures and thetemporal distances from the current picture to the respective tworeference pictures are equal to each other, mirror-symmetricalbi-directional motion vectors are derived in the first pattern matching.

MV Derivation > FRUC > Template Matching

In the second pattern matching (template matching), pattern matching isperformed between a block in a reference picture and a template in thecurrent picture (the template is a block neighboring the current blockin the current picture (the neighboring block is, for example, an upperand/or left neighboring block(s))). Accordingly, in the second patternmatching, the block neighboring the current block in the current pictureis used as the determined region for calculating the evaluation value ofthe above-described candidate.

FIG. 24 is a conceptual diagram for illustrating one example of patternmatching (template matching) between a template in a current picture anda block in a reference picture. As illustrated in FIG. 24 , in thesecond pattern matching, the motion vector of the current block (Curblock) is derived by estimating, in the reference picture (Ref0), theblock which best matches the block neighboring the current block in thecurrent picture (Cur Pic). More specifically, it is possible that thedifference between a reconstructed image in an encoded region whichneighbors both left and above or either left or above and areconstructed image which is in a corresponding region in the encodedreference picture (Ref0) and is specified by an MV candidate is derived,an evaluation value is calculated using the value of the obtaineddifference, and the MV candidate which yields the best evaluation valueamong a plurality of MV candidates is selected as the best MV candidate.

Such information indicating whether to apply the FRUC mode (referred toas, for example, a FRUC flag) may be signaled at the CU level. Inaddition, when the FRUC mode is applied (for example, when a FRUC flagis true), information indicating an applicable pattern matching method(either the first pattern matching or the second pattern matching) maybe signaled at the CU level. It is to be noted that the signaling ofsuch information does not necessarily need to be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

MV Derivation > Affine Mode

Next, the affine mode for deriving a motion vector in units of asub-block based on motion vectors of a plurality of neighboring blocksis described. This mode is also referred to as an affine motioncompensation prediction mode.

FIG. 25A is a conceptual diagram for illustrating one example ofderiving a motion vector of each sub-block based on motion vectors of aplurality of neighboring blocks. In FIG. 25A, the current block includessixteen 4×4 sub-blocks. Here, motion vector V₀ at an upper-left cornercontrol point in the current block is derived based on a motion vectorof a neighboring block, and likewise, motion vector V₁ at an upper-rightcorner control point in the current block is derived based on a motionvector of a neighboring sub-block. Two motion vectors v₀ and v₁ may beprojected according to an expression (1A) indicated below, and motionvectors (v_(x), v_(y)) for the respective sub-blocks in the currentblock may be derived.

[Math. 1]

$\begin{matrix}\left\{ \begin{matrix}{\text{v}_{\text{x}} = \frac{\left( {\text{v}_{1\text{x}} - \text{v}_{0\text{x}}} \right)}{\text{w}}\text{x} - \frac{\left( {\text{v}_{1\text{y}} - \text{v}_{0\text{y}}} \right)}{\text{w}}\text{y}\mspace{6mu} + \mspace{6mu}\text{v}_{0\text{x}}} \\{\text{v}_{\text{y}} = \frac{\left( {\text{v}_{1\text{y}} - \text{v}_{0\text{y}}} \right)}{\text{w}}\text{x} - \frac{\left( {\text{v}_{1\text{x}} - \text{v}_{0\text{x}}} \right)}{\text{w}}\text{y}\mspace{6mu} + \mspace{6mu}\text{v}_{0\text{y}}}\end{matrix} \right) & \text{­­­(1A)}\end{matrix}$

Here, x and y indicate the horizontal position and the vertical positionof the sub-block, respectively, and w indicates a determined weightingcoefficient. The determined weighting coefficient may be predetermined.

Such information indicating the affine mode (for example, referred to asan affine flag) may be signaled at the CU level. It is to be noted thatthe signaling of the information indicating the affine mode does notnecessarily need to be performed at the CU level, and may be performedat another level (for example, at the sequence level, picture level,slice level, tile level, CTU level, or sub-block level).

In addition, the affine mode may include several modes for differentmethods for deriving motion vectors at the upper-left and upper-rightcorner control points. For example, the affine mode include two modeswhich are the affine inter mode (also referred to as an affine normalinter mode) and the affine merge mode.

MV Derivation > Affine Mode

FIG. 25B is a conceptual diagram for illustrating one example ofderiving a motion vector of each sub-block in affine mode in which threecontrol points are used. In FIG. 25B, the current block includes sixteen4×4 blocks. Here, motion vector V₀ at the upper-left corner controlpoint for the current block is derived based on a motion vector of aneighboring block, and likewise, motion vector V₁ at the upper-rightcorner control point for the current block is derived based on a motionvector of a neighboring block, and motion vector V₂ at the lower-leftcorner control point for the current block is derived based on a motionvector of a neighboring block. Three motion vectors v₀, v₁, and v₂ maybe projected according to an expression (1B) indicated below, and motionvectors (v_(x), v_(y)) for the respective sub-blocks in the currentblock may be derived.

[Math. 2]

$\begin{matrix}\left\{ \begin{matrix}{\text{v}_{\text{x}} = \frac{\left( {\text{v}_{1\text{x}} - \text{v}_{0\text{x}}} \right)}{\text{w}}\text{x} - \frac{\left( {\text{v}_{2\text{x}} - \text{v}_{0\text{x}}} \right)}{\text{h}}\text{y}\mspace{6mu} + \mspace{6mu}\text{v}_{0\text{x}}} \\{\text{v}_{\text{y}} = \frac{\left( {\text{v}_{1\text{y}} - \text{v}_{0\text{y}}} \right)}{\text{w}}\text{x} - \frac{\left( {\text{v}_{2\text{x}} - \text{v}_{0\text{y}}} \right)}{\text{h}}\text{y}\mspace{6mu} + \mspace{6mu}\text{v}_{0\text{y}}}\end{matrix} \right) & \text{­­­(1B)}\end{matrix}$

Here, x and y indicate the horizontal position and the vertical positionof the center of the sub-block, respectively, w indicates the width ofthe current block, and h indicates the height of the current block.

Affine modes in which different numbers of control points (for example,two and three control points) are used may be switched and signaled atthe CU level. It is to be noted that information indicating the numberof control points in affine mode used at the CU level may be signaled atanother level (for example, the sequence level, picture level, slicelevel, tile level, CTU level, or sub-block level).

In addition, such an affine mode in which three control points are usedmay include different methods for deriving motion vectors at theupper-left, upper-right, and lower-left corner control points. Forexample, the affine modes include two modes which are the affine intermode (also referred to as the affine normal inter mode) and the affinemerge mode.

MV Derivation > Affine Merge Mode

FIG. 26A, FIG. 26B, and FIG. 26C are conceptual diagrams forillustrating the affine merge mode.

As illustrated in FIG. 26A, in the affine merge mode, for example,motion vector predictors at respective control points of a current blockare calculated based on a plurality of motion vectors corresponding toblocks encoded according to the affine mode among encoded block A(left), block B (upper), block C (upper-right), block D (lower-left),and block E (upper-left) which neighbor the current block. Morespecifically, encoded block A (left), block B (upper), block C(upper-right), block D (lower-left), and block E (upper-left) arechecked in the listed order, and the first effective block encodedaccording to the affine mode is identified. Motion vector predictors atthe control points of the current block are calculated based on aplurality of motion vectors corresponding to the identified block.

For example, as illustrated in FIG. 26B, when block A which neighbors tothe left of the current block has been encoded according to an affinemode in which two control points are used, motion vectors v₃ and v₄projected at the upper-left corner position and the upper-right cornerposition of the encoded block including block A are derived. Motionvector predictor v₀ at the upper-left corner control point of thecurrent block and motion vector predictor v₁ at the upper-right cornercontrol point of the current block are then calculated from derivedmotion vectors v₃ and v₄.

For example, as illustrated in FIG. 26C, when block A which neighbors tothe left of the current block has been encoded according to an affinemode in which three control points are used, motion vectors v₃, v₄, andv₅ projected at the upper-left corner position, the upper-right cornerposition, and the lower-left corner position of the encoded blockincluding block A are derived. Motion vector predictor v₀ at theupper-left corner control point of the current block, motion vectorpredictor v₁ at the upper-right corner control point of the currentblock, and motion vector predictor v₂ at the lower-left corner controlpoint of the current block are then calculated from derived motionvectors v₃, _(V4), and v₅.

It is to be noted that this method for deriving motion vector predictorsmay be used to derive motion vector predictors of the respective controlpoints of the current block in Step Sj_1 in FIG. 29 described later.

FIG. 27 is a flow chart illustrating one example of the affine mergemode.

In affine merge mode as illustrated, first, inter predictor 126 derivesMV predictors of respective control points of a current block (StepSk_1). The control points are an upper-left corner point of the currentblock and an upper-right corner point of the current block asillustrated in FIG. 25A, or an upper-left corner point of the currentblock, an upper-right corner point of the current block, and alower-left corner point of the current block as illustrated in FIG. 25B.

In other words, as illustrated in FIG. 26A, inter predictor 126 checksencoded block A (left), block B (upper), block C (upper-right), block D(lower-left), and block E (upper-left) in the listed order, andidentifies the first effective block encoded according to the affinemode.

When block A is identified and block A has two control points, asillustrated in FIG. 26B, inter predictor 126 calculates motion vector v₀at the upper-left corner control point of the current block and motionvector v₁ at the upper-right corner control point of the current blockfrom motion vectors v₃ and v₄ at the upper-left corner and theupper-right corner of the encoded block including block A. For example,inter predictor 126 calculates motion vector v₀ at the upper-left cornercontrol point of the current block and motion vector v₁ at theupper-right corner control point of the current block by projectingmotion vectors v₃ and v₄ at the upper-left corner and the upper-rightcorner of the encoded block onto the current block.

Alternatively, when block A is identified and block A has three controlpoints, as illustrated in FIG. 26C, inter predictor 126 calculatesmotion vector v₀ at the upper-left corner control point of the currentblock, motion vector v₁ at the upper-right corner control point of thecurrent block, and motion vector v₂ at the lower-left corner controlpoint of the current block from motion vectors v₃, v₄, and v₅ at theupper-left corner, the upper-right corner, and the lower-left corner ofthe encoded block including block A. For example, inter predictor 126calculates motion vector v₀ at the upper-left corner control point ofthe current block, motion vector v₁ at the upper-right corner controlpoint of the current block, and motion vector v₂ at the lower-leftcorner control point of the current block by projecting motion vectorsv₃, v₄, and v₅ at the upper-left corner, the upper-right corner, and thelower-left corner of the encoded block onto the current block.

Next, inter predictor 126 performs motion compensation of each of aplurality of sub-blocks included in the current block. In other words,inter predictor 126 calculates, for each of the plurality of sub-blocks,a motion vector of the sub-block as an affine MV, by using either (i)two motion vector predictors v₀ and v₁ and the expression (1A) describedabove or (ii) three motion vector predictors v₀, v₁, and v₂ and theexpression (1B) described above (Step Sk_2). Inter predictor 126 thenperforms motion compensation of the sub-blocks using these affine MVsand encoded reference pictures (Step Sk_3). As a result, motioncompensation of the current block is performed to generate a predictionimage of the current block.

MV Derivation > Affine Inter Mode

FIG. 28A is a conceptual diagram for illustrating an affine inter modein which two control points are used.

In the affine inter mode, as illustrated in FIG. 28A, a motion vectorselected from motion vectors of encoded block A, block B, and block Cwhich neighbor the current block is used as motion vector predictor v₀at the upper-left corner control point of the current block. Likewise, amotion vector selected from motion vectors of encoded block D and blockE which neighbor the current block is used as motion vector predictor v₁at the upper-right corner control point of the current block.

FIG. 28B is a conceptual diagram for illustrating an affine inter modein which three control points are used.

In the affine inter mode, as illustrated in FIG. 28B, a motion vectorselected from motion vectors of encoded block A, block B, and block Cwhich neighbor the current block is used as motion vector predictor v₀at the upper-left corner control point of the current block. Likewise, amotion vector selected from motion vectors of encoded block D and blockE which neighbor the current block is used as motion vector predictor v₁at the upper-right corner control point of the current block.Furthermore, a motion vector selected from motion vectors of encodedblock F and block G which neighbor the current block is used as motionvector predictor v₂ at the lower-left corner control point of thecurrent block.

FIG. 29 is a flow chart illustrating one example of an affine intermode.

In the affine inter mode as illustrated, first, inter predictor 126derives MV predictors (v₀, v₁) or (v₀, v₁, v₂) of respective two orthree control points of a current block (Step Sj_1). The control pointsare an upper-left corner point of the current block and an upper-rightcorner point of the current block as illustrated in FIG. 25A, or anupper-left corner point of the current block, an upper-right cornerpoint of the current block, and a lower-left corner point of the currentblock as illustrated in FIG. 25B.

In other words, inter predictor 126 derives the motion vector predictors(v₀, v₁) or (v₀, v₁, v₂) of respective two or three control points ofthe current block by selecting motion vectors of any of the blocks amongencoded blocks in the vicinity of the respective control points of thecurrent block illustrated in either FIG. 28A or FIG. 28B. At this time,inter predictor 126 encodes, in a stream, motion vector predictorselection information for identifying the selected two motion vectors.

For example, inter predictor 126 may determine, using a cost evaluationor the like, the block from which a motion vector as a motion vectorpredictor at a control point is selected from among encoded blocksneighboring the current block, and may describe, in a bitstream, a flagindicating which motion vector predictor has been selected.

Next, inter predictor 126 performs motion estimation (Step Sj_3 andSj_4) while updating a motion vector predictor selected or derived inStep Sj_1 (Step Sj_2). In other words, inter predictor 126 calculates,as an affine MV, a motion vector of each of sub-blocks which correspondsto an updated motion vector predictor, using either the expression (1A)or expression (1B) described above (Step Sj_3). Inter predictor 126 thenperforms motion compensation of the sub-blocks using these affine MVsand encoded reference pictures (Step Sj_4). As a result, for example,inter predictor 126 determines the motion vector predictor which yieldsthe smallest cost as the motion vector at a control point in a motionestimation loop (Step Sj_5). At this time, inter predictor 126 furtherencodes, in the stream, the difference value between the determined MVand the motion vector predictor as an MV difference.

Lastly, inter predictor 126 generates a prediction image for the currentblock by performing motion compensation of the current block using thedetermined MV and the encoded reference picture (Step Sj_6).

MV Derivation > Affine Inter Mode

When affine modes in which different numbers of control points (forexample, two and three control points) are used may be switched andsignaled at the CU level, the number of control points in an encodedblock and the number of control points in a current block may bedifferent from each other. FIG. 30A and FIG. 30B are conceptual diagramsfor illustrating methods for deriving motion vector predictors atcontrol points when the number of control points in an encoded block andthe number of control points in a current block are different from eachother.

For example, as illustrated in FIG. 30A, when a current block has threecontrol points at the upper-left corner, the upper-right corner, and thelower-left corner, and block A which neighbors to the left of thecurrent block has been encoded according to an affine mode in which twocontrol points are used, motion vectors V₃ and v₄ projected at theupper-left corner position and the upper-right corner position in theencoded block including block A are derived. Motion vector predictor v₀at the upper-left corner control point of the current block and motionvector predictor v₁ at the upper-right corner control point of thecurrent block are then calculated from derived motion vectors v₃ and v₄.Furthermore, motion vector predictor v₂ at the lower-left corner controlpoint is calculated from derived motion vectors v₀ and v₁.

For example, as illustrated in FIG. 30B, when a current block has twocontrol points at the upper-left corner and the upper-right corner, andblock A which neighbors to the left of the current block has beenencoded according to the affine mode in which three control points areused, motion vectors v₃, v₄, and v₅ projected at the upper-left cornerposition, the upper-right corner position, and the lower-left cornerposition in the encoded block including block A are derived. Motionvector predictor v₀ at the upper-left corner control point of thecurrent block and motion vector predictor v₁ at the upper-right cornercontrol point of the current block are then calculated from derivedmotion vectors v₃, v₄, and v₅.

It is to be noted that this method for deriving motion vector predictorsmay be used to derive motion vector predictors of the respective controlpoints of the current block in Step Sj_1 in FIG. 29 .

MV Derivation > DMVR

FIG. 31A is a flow chart illustrating a relationship between the mergemode and DMVR.

Inter predictor 126 derives a motion vector of a current block accordingto the merge mode (Step S1_1). Next, inter predictor 126 determineswhether to perform estimation of a motion vector, that is, motionestimation (Step S1_2). Here, when determining not to perform motionestimation (No in Step S1_2), inter predictor 126 determines the motionvector derived in Step S1_1 as the final motion vector for the currentblock (Step S1_4). In other words, in this case, the motion vector ofthe current block is determined according to the merge mode.

When determining to perform motion estimation in Step S1_1 (Yes in StepS1_2), inter predictor 126 derives the final motion vector for thecurrent block by estimating a surrounding region of the referencepicture specified by the motion vector derived in Step S1_1 (Step S1_3).In other words, in this case, the motion vector of the current block isdetermined according to the DMVR.

FIG. 31B is a conceptual diagram for illustrating one example of a DMVRprocess for determining an MV.

First, (for example, in merge mode) the best Motion Vector Predictor(MVP) which has been set to the current block is determined to be an MVcandidate. A reference pixel is identified from a first referencepicture (L0) which is an encoded picture in the L0 direction accordingto an MV candidate (L0). Likewise, a reference pixel is identified froma second reference picture (L1) which is an encoded picture in the L1direction according to an MV candidate (L1). A template is generated bycalculating an average of these reference pixels.

Next, each of the surrounding regions of MV candidates of the firstreference picture (L0) and the second reference picture (L1) areestimated, and the MV which yields the smallest cost is determined to bethe final MV. It is to be noted that the cost value may be calculated,for example, using a difference value between each of the pixel valuesin the template and a corresponding one of the pixel values in theestimation region, the values of MV candidates, etc.

It is to be noted that the processes, configurations, and operationsdescribed here typically are basically common between the encoder and adecoder to be described later.

Exactly the same example processes described here do not always need tobe performed. Any process for enabling derivation of the final MV byestimation in surrounding regions of MV candidates may be used.

Motion Compensation > BIO/OBMC

Motion compensation involves a mode for generating a prediction image,and correcting the prediction image. The mode is, for example, BIO andOBMC to be described later.

FIG. 32 is a flow chart illustrating one example of generation of aprediction image.

Inter predictor 126 generates a prediction image (Step Sm_1), andcorrects the prediction image, for example, according to any of themodes described above (Step Sm_2).

FIG. 33 is a flow chart illustrating another example of generation of aprediction image.

Inter predictor 126 determines a motion vector of a current block (StepSn_1). Next, inter predictor 126 generates a prediction image (StepSn_2), and determines whether to perform a correction process (StepSn_3). Here, when determining to perform a correction process (Yes inStep Sn_3), inter predictor 126 generates the final prediction image bycorrecting the prediction image (Step Sn_4). When determining not toperform a correction process (No in Step Sn_3), inter predictor 126outputs the prediction image as the final prediction image withoutcorrecting the prediction image (Step Sn_5).

In addition, motion compensation involves a mode for correcting aluminance of a prediction image when generating the prediction image.The mode is, for example, LIC to be described later.

FIG. 34 is a flow chart illustrating another example of generation of aprediction image.

Inter predictor 126 derives a motion vector of a current block (StepSo_1). Next, inter predictor 126 determines whether to perform aluminance correction process (Step So_2). Here, when determining toperform a luminance correction process (Yes in Step So_2), interpredictor 126 generates the prediction image while performing aluminance correction process (Step So_3). In other words, the predictionimage is generated using LIC. When determining not to perform aluminance correction process (No in Step So_2), inter predictor 126generates a prediction image by performing normal motion compensationwithout performing a luminance correction process (Step So_4).

Motion Compensation > OBMC

It is to be noted that an inter prediction signal may be generated usingmotion information for a neighboring block in addition to motioninformation for the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated in units of asub-block in the current block by performing a weighted addition of aprediction signal based on motion information obtained from motionestimation (in the reference picture) and a prediction signal based onmotion information for a neighboring block (in the current picture).Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In OBMC mode, information indicating a sub-block size for OBMC (referredto as, for example, an OBMC block size) may be signaled at the sequencelevel. Moreover, information indicating whether to apply the OBMC mode(referred to as, for example, an OBMC flag) may be signaled at the CUlevel. It is to be noted that the signaling of such information does notnecessarily need to be performed at the sequence level and CU level, andmay be performed at another level (for example, at the picture level,slice level, tile level, CTU level, or sub-block level).

Examples of the OBMC mode will be described in further detail. FIGS. 35and 36 are a flow chart and a conceptual diagram for illustrating anoutline of a prediction image correction process performed by an OBMCprocess.

First, as illustrated in FIG. 36 , a prediction image (Pred) is obtainedthrough normal motion compensation using a motion vector (MV) assignedto the processing target (current) block. In FIG. 36 , the arrow “MV”points a reference picture, and indicates what the current block of thecurrent picture refers to in order to obtain a prediction image.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) which has been already derived for the encoded blockneighboring to the left of the current block to the current block(re-using the motion vector for the current block). The motion vector(MV _L) is indicated by an arrow “MV_L” indicating a reference picturefrom a current block. A first correction of a prediction image isperformed by overlapping two prediction images Pred and Pred_L. Thisprovides an effect of blending the boundary between neighboring blocks.

Likewise, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) which has been already derived for the encoded blockneighboring above the current block to the current block (re-using themotion vector for the current block). The motion vector (MV_U) isindicated by an arrow “MV - U” indicating a reference picture from acurrent block. A second correction of a prediction image is performed byoverlapping the prediction image Pred_U to the prediction images (forexample, Pred and Pred_L) on which the first correction has beenperformed. This provides an effect of blending the boundary betweenneighboring blocks. The prediction image obtained by the secondcorrection is the one in which the boundary between the neighboringblocks has been blended (smoothed), and thus is the final predictionimage of the current block.

Although the above example is a two-path correction method using leftand upper neighboring blocks, it is to be noted that the correctionmethod may be three- or more-path correction method using also the rightneighboring block and/or the lower neighboring block.

It is to be noted that the region in which such overlapping is performedmay be only part of a region near a block boundary instead of the pixelregion of the entire block.

It is to be noted that the prediction image correction process accordingto OBMC for obtaining one prediction image Pred from one referencepicture by overlapping additional prediction image Pred_L and Pred_Uhave been described above. However, when a prediction image is correctedbased on a plurality of reference images, a similar process may beapplied to each of the plurality of reference pictures. In such a case,after corrected prediction images are obtained from the respectivereference pictures by performing OBMC image correction based on theplurality of reference pictures, the obtained corrected predictionimages are further overlapped to obtain the final prediction image.

It is to be noted that, in OBMC, the unit of a current block may be theunit of a prediction block or the unit of a sub-block obtained byfurther splitting the prediction block.

One example of a method for determining whether to apply an OBMC processis a method for using an obmc_flag which is a signal indicating whetherto apply an OBMC process. As one specific example, an encoder determineswhether the current block belongs to a region having complicated motion.The encoder sets the obmc_flag to a value of “1” when the block belongsto a region having complicated motion and applies an OBMC process whenencoding, and sets the obmc_flag to a value of “0” when the block doesnot belong to a region having complicated motion and encodes the blockwithout applying an OBMC process. The decoder switches betweenapplication and non-application of an OBMC process by decoding theobmc_flag written in the stream (for example, a compressed sequence) anddecoding the block by switching between the application andnon-application of the OBMC process in accordance with the flag value.

Inter predictor 126 generates one rectangular prediction image for arectangular current block in the above example. However, inter predictor126 may generate a plurality of prediction images each having a shapedifferent from a rectangle for the rectangular current block, and maycombine the plurality of prediction images to generate the finalrectangular prediction image. The shape different from a rectangle maybe, for example, a triangle.

FIG. 37 is a conceptual diagram for illustrating generation of twotriangular prediction images.

Inter predictor 126 generates a triangular prediction image byperforming motion compensation of a first partition having a triangularshape in a current block by using a first MV of the first partition, togenerate a triangular prediction image. Likewise, inter predictor 126generates a triangular prediction image by performing motioncompensation of a second partition having a triangular shape in acurrent block by using a second MV of the second partition, to generatea triangular prediction image. Inter predictor 126 then generates aprediction image having the same rectangular shape as the rectangularshape of the current block by combining these prediction images.

It is to be noted that, although the first partition and the secondpartition are triangles in the example illustrated in FIG. 37 , thefirst partition and the second partition may be trapezoids, or othershapes different from each other. Furthermore, although the currentblock includes two partitions in the example illustrated in FIG. 37 ,the current block may include three or more partitions.

In addition, the first partition and the second partition may overlapwith each other. In other words, the first partition and the secondpartition may include the same pixel region. In this case, a predictionimage for a current block may be generated using a prediction image inthe first partition and a prediction image in the second partition.

In addition, although an example in which a prediction image isgenerated for each of two partitions using inter prediction, aprediction image may be generated for at least one partition using intraprediction.

Motion Compensation > BIO

Next, a method for deriving a motion vector is described. First, a modefor deriving a motion vector based on a model assuming uniform linearmotion will be described. This mode is also referred to as abi-directional optical flow (BIO) mode.

FIG. 38 is a conceptual diagram for illustrating a model assuminguniform linear motion. In FIG. 38 , (vx, vy) indicates a velocityvector, and τ0 and τ1 indicate temporal distances between a currentpicture (Cur Pic) and two reference pictures (Ref0, Ref1). (MVx0, MVy0)indicate motion vectors corresponding to reference picture Ref0, and(MVx1, MVy1) indicate motion vectors corresponding to reference pictureRef1.

Here, under the assumption of uniform linear motion exhibited byvelocity vectors (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τo, v_(y)τ₀) and (-v_(x)τ₁, -v_(y)τ₁),respectively, and the following optical flow equation (2) may beemployed.

[Math. 3]

$\begin{matrix}{{{\partial\text{I}^{(\text{k})}}/{\partial\text{t}\mspace{6mu}\text{+}\mspace{6mu}\text{v}_{\text{x}}\mspace{6mu}{{\partial\text{I}^{(\text{k})}}/{\partial\text{x}}}}}\mspace{6mu} + \mspace{6mu} v_{\text{y}}\mspace{6mu}{{\partial\text{I}^{(\text{k})}}/{\partial\text{y}\mspace{6mu}\text{=}\mspace{6mu}\text{0}\text{.}}}} & \text{­­­(2)}\end{matrix}$

Here, I(k) indicates a motion-compensated luma value of referencepicture k (k = 0, 1). This optical flow equation shows that the sum of(i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference image, and (iii) the product of the vertical velocity andthe vertical component of the spatial gradient of a reference image isequal to zero. A motion vector of each block obtained from, for example,a merge list may be corrected in units of a pixel, based on acombination of the optical flow equation and Hermite interpolation.

It is to be noted that a motion vector may be derived on the decoderside using a method other than deriving a motion vector based on a modelassuming uniform linear motion. For example, a motion vector may bederived in units of a sub-block based on motion vectors of neighboringblocks.

Motion Compensation > LIC

Next, an example of a mode in which a prediction image (prediction) isgenerated by using a local illumination compensation (LIC) process willbe described.

FIG. 39 is a conceptual diagram for illustrating one example of aprediction image generation method using a luminance correction processperformed by a LIC process.

First, an MV is derived from an encoded reference picture, and areference image corresponding to the current block is obtained.

Next, information indicating how the luma value changed between thereference picture and the current picture is extracted for the currentblock. This extraction is performed based on the luma pixel values forthe encoded left neighboring reference region (surrounding referenceregion) and the encoded upper neighboring reference region (surroundingreference region), and the luma pixel value at the correspondingposition in the reference picture specified by the derived MV. Aluminance correction parameter is calculated by using the informationindicating how the luma value changed.

The prediction image for the current block is generated by performing aluminance correction process in which the luminance correction parameteris applied to the reference image in the reference picture specified bythe MV.

It is to be noted that the shape of the surrounding reference regionillustrated in FIG. 39 is just one example; the surrounding referenceregion may have a different shape.

Moreover, although the process in which a prediction image is generatedfrom a single reference picture has been described here, cases in whicha prediction image is generated from a plurality of reference picturescan be described in the same manner. The prediction image may begenerated after performing a luminance correction process of thereference images obtained from the reference pictures in the same manneras described above.

One example of a method for determining whether to apply a LIC processis a method for using a lic_flag which is a signal indicating whether toapply the LIC process. As one specific example, the encoder determineswhether the current block belongs to a region having a luminance change.The encoder sets the lic_flag to a value of “1” when the block belongsto a region having a luminance change and applies a LIC process whenencoding, and sets the lic_flag to a value of “0” when the block doesnot belong to a region having a luminance change and encodes the currentblock without applying a LIC process. The decoder may decode thelic_flag written in the stream and decode the current block by switchingbetween application and non-application of a LIC process in accordancewith the flag value.

One example of a different method of determining whether to apply a LICprocess is a determining method in accordance with whether a LIC processwas applied to a surrounding block. In one specific example, when themerge mode is used on the current block, whether a LIC process wasapplied in the encoding of the surrounding encoded block selected uponderiving the MV in the merge mode process is determined. According tothe result, encoding is performed by switching between application andnon-application of a LIC process. It is to be noted that, also in thisexample, the same processes are applied in processes at the decoderside.

An embodiment of the luminance correction (LIC) process described withreference to FIG. 39 is described in detail below.

First, inter predictor 126 derives a motion vector for obtaining areference image corresponding to a current block to be encoded from areference picture which is an encoded picture.

Next, inter predictor 126 extracts information indicating how the lumavalue of the reference picture has been changed to the luma value of thecurrent picture, using the luma pixel value of an encoded surroundingreference region which neighbors to the left of or above the currentblock and the luma value in the corresponding position in the referencepicture specified by a motion vector, and calculates a luminancecorrection parameter. For example, it is assumed that the luma pixelvalue of a given pixel in the surrounding reference region in thecurrent picture is p0, and that the luma pixel value of the pixelcorresponding to the given pixel in the surrounding reference region inthe reference picture is p1. Inter predictor 126 calculates coefficientsA and B for optimizing A × p1 + B = p0 as the luminance correctionparameter for a plurality of pixels in the surrounding reference region.

Next, inter predictor 126 performs a luminance correction process usingthe luminance correction parameter for the reference image in thereference picture specified by the motion vector, to generate aprediction image for the current block. For example, it is assumed thatthe luma pixel value in the reference image is p2, and that theluminance-corrected luma pixel value of the prediction image is p3.Inter predictor 126 generates the prediction image after being subjectedto the luminance correction process by calculating A × p2 + B = p3 foreach of the pixels in the reference image.

It is to be noted that the shape of the surrounding reference regionillustrated in FIG. 39 is one example; a different shape other than theshape of the surrounding reference region may be used. In addition, partof the surrounding reference region illustrated in FIG. 39 may be used.For example, a region having a determined number of pixels extractedfrom each of an upper neighboring pixel and a left neighboring pixel maybe used as a surrounding reference region. The determined number ofpixels may be predetermined.

In addition, the surrounding reference region is not limited to a regionwhich neighbors the current block, and may be a region which does notneighbor the current block. In the example illustrated in FIG. 39 , thesurrounding reference region in the reference picture is a regionspecified by a motion vector in a current picture, from a surroundingreference region in the current picture. However, a region specified byanother motion vector is also possible. For example, the other motionvector may be a motion vector in a surrounding reference region in thecurrent picture.

Although operations performed by encoder 100 have been described here,it is to be noted that decoder 200 typically performs similaroperations.

It is to be noted that the LIC process may be applied not only to theluma but also to chroma. At this time, a correction parameter may bederived individually for each of Y, Cb, and Cr, or a common correctionparameter may be used for any of Y, Cb, and Cr.

In addition, the LIC process may be applied in units of a sub-block. Forexample, a correction parameter may be derived using a surroundingreference region in a current sub-block and a surrounding referenceregion in a reference sub-block in a reference picture specified by anMV of the current sub-block.

Prediction Controller

Inter predictor 128 selects one of an intra prediction signal (a signaloutput from intra predictor 124) and an inter prediction signal (asignal output from inter predictor 126), and outputs the selected signalto subtractor 104 and adder 116 as a prediction signal.

As illustrated in FIG. 1 , in various kinds of encoder examples,prediction controller 128 may output a prediction parameter which isinput to entropy encoder 110. Entropy encoder 110 may generate anencoded bitstream (or a sequence), based on the prediction parameterwhich is input from prediction controller 128 and quantized coefficientswhich are input from quantizer 108. The prediction parameter may be usedin a decoder. The decoder may receive and decode the encoded bitstream,and perform the same processes as the prediction processes performed byintra predictor 124, inter predictor 126, and prediction controller 128.The prediction parameter may include (i) a selection prediction signal(for example, a motion vector, a prediction type, or a prediction modeused by intra predictor 124 or inter predictor 126), or (ii) an optionalindex, a flag, or a value which is based on a prediction processperformed in each of intra predictor 124, inter predictor 126, andprediction controller 128, or which indicates the prediction process.

Mounting Example of Encoder

FIG. 40 is a block diagram illustrating a mounting example of encoder100. Encoder 100 includes processor a1 and memory a2. For example, theplurality of constituent elements of encoder 100 illustrated in FIG. 1are mounted on processor a1 and memory a2 illustrated in FIG. 40 .

Processor a1 is circuitry which performs information processing and isaccessible to memory a2. For example, processor a1 is dedicated orgeneral electronic circuitry which encodes a video. Processor a1 may bea processor such as a CPU. In addition, processor a1 may be an aggregateof a plurality of electronic circuits. In addition, for example,processor a1 may take the roles of two or more constituent elements outof the plurality of constituent elements of encoder 100 illustrated inFIG. 1 , etc.

Memory a2 is dedicated or general memory for storing information that isused by processor a1 to encode a video. Memory a2 may be electroniccircuitry, and may be connected to processor a1. In addition, memory a2may be included in processor a1. In addition, memory a2 may be anaggregate of a plurality of electronic circuits. In addition, memory a2may be a magnetic disc, an optical disc, or the like, or may berepresented as a storage, a recording medium, or the like. In addition,memory a2 may be non-volatile memory, or volatile memory.

For example, memory a2 may store a video to be encoded or a bitstreamcorresponding to an encoded video. In addition, memory a2 may store aprogram for causing processor a1 to encode a video.

In addition, for example, memory a2 may take the roles of two or moreconstituent elements for storing information out of the plurality ofconstituent elements of encoder 100 illustrated in FIG. 1 , etc. Forexample, memory a2 may take the roles of block memory 118 and framememory 122 illustrated in FIG. 1 . More specifically, memory a2 maystore a reconstructed block, a reconstructed picture, etc.

It is to be noted that, in encoder 100, all of the plurality ofconstituent elements indicated in FIG. 1 , etc. may not be implemented,and all the processes described above may not be performed. Part of theconstituent elements indicated in FIG. 1 , etc. may be included inanother device, or part of the processes described above may beperformed by another device.

Decoder

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output, for example, from encoder 100 described above will bedescribed. FIG. 41 is a block diagram illustrating a configuration ofdecoder 200 according to an embodiment. Decoder 200 is a video decoderwhich decodes a video in units of a block.

As illustrated in FIG. 41 , decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is implemented as, for example, a generic processor andmemory. In this case, when a software program stored in the memory isexecuted by the processor, the processor functions as entropy decoder202, inverse quantizer 204, inverse transformer 206, adder 208, loopfilter 212, intra predictor 216, inter predictor 218, and predictioncontroller 220. Alternatively, decoder 200 may be implemented as one ormore dedicated electronic circuits corresponding to entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220.

Hereinafter, an overall flow of processes performed by decoder 200 isdescribed, and then each of constituent elements included in decoder 200will be described.

Overall Flow of Decoding Process

FIG. 42 is a flow chart illustrating one example of an overall decodingprocess performed by decoder 200.

First, entropy decoder 202 of decoder 200 identifies a splitting patternof a block having a fixed size (for example, 128×128 pixels) (StepSp_1). This splitting pattern is a splitting pattern selected by encoder100. Decoder 200 then performs processes of Step Sp_2 to Sp_6 for eachof a plurality of blocks of the splitting pattern.

In other words, entropy decoder 202 decodes (specifically,entropy-decodes) encoded quantized coefficients and a predictionparameter of a current block to be decoded (also referred to as acurrent block) (Step Sp_2).

Next, inverse quantizer 204 performs inverse quantization of theplurality of quantized coefficients and inverse transformer 206 performsinverse transform of the result, to restore a plurality of predictionresiduals (that is, a difference block) (Step Sp_3).

Next, the prediction processor including all or part of intra predictor216, inter predictor 218, and prediction controller 220 generates aprediction signal (also referred to as a prediction block) of thecurrent block (Step Sp_4).

Next, adder 208 adds the prediction block to the difference block togenerate a reconstructed image (also referred to as a decoded imageblock) of the current block (Step Sp_5).

When the reconstructed image is generated, loop filter 212 performsfiltering of the reconstructed image (Step Sp_6).

Decoder 200 then determines whether decoding of the entire picture hasbeen finished (Step Sp_7). When determining that the decoding has notyet been finished (No in Step Sp_7), decoder 200 repeatedly executes theprocesses starting with Step Sp_1.

As illustrated, the processes of Steps Sp_1 to Sp_7 are performedsequentially by decoder 200. Alternatively, two or more of the processesmay be performed in parallel, the processing order of the two or more ofthe processes may be modified, etc.

Entropy Decoder

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204. Entropydecoder 202 may output a prediction parameter included in an encodedbitstream (see FIG. 1 ) to intra predictor 216, inter predictor 218, andprediction controller 220. Intra predictor 216, inter predictor 218, andprediction controller 220 in an embodiment are capable of executing thesame prediction processes as those performed by intra predictor 124,inter predictor 126, and prediction controller 128 at the encoder side.

Inverse Quantizer

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block) whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock, based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedtransform coefficients of the current block to inverse transformer 206.

Inverse Transformer

Inverse transformer 206 restores prediction errors by inversetransforming the transform coefficients which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesthat EMT or AMT is to be applied (for example, when an AMT flag istrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates that NSST is to be applied, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

Adder

Adder 208 reconstructs the current block by adding prediction errorswhich are inputs from inverse transformer 206 and prediction sampleswhich are inputs from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

Block Memory

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) and to bereferred to in intra prediction. More specifically, block memory 210stores reconstructed blocks output from adder 208.

Loop Filter

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214,display device, etc.

When information indicating ON or OFF of an ALF parsed from an encodedbitstream indicates that an ALF is ON, one filter from among a pluralityof filters is selected based on direction and activity of localgradients, and the selected filter is applied to the reconstructedblock.

Frame Memory

Frame memory 214 is, for example, storage for storing reference picturesfor use in inter prediction, and is also referred to as a frame buffer.More specifically, frame memory 214 stores a reconstructed blockfiltered by loop filter 212.

Prediction Processor (Intra Predictor, Inter Predictor, PredictionController)

FIG. 43 is a flow chart illustrating one example of a process performedby a prediction processor of decoder 200. It is to be noted that theprediction processor includes all or part of the following constituentelements: intra predictor 216; inter predictor 218; and predictioncontroller 220.

The prediction processor generates a prediction image of a current block(Step Sq_1). This prediction image is also referred to as a predictionsignal or a prediction block. It is to be noted that the predictionsignal is, for example, an intra prediction signal or an interprediction signal. Specifically, the prediction processor generates theprediction image of the current block using a reconstructed image whichhas been already obtained through generation of a prediction block,generation of a difference block, generation of a coefficient block,restoring of a difference block, and generation of a decoded imageblock.

The reconstructed image may be, for example, an image in a referencepicture, or an image of a decoded block in a current picture which isthe picture including the current block. The decoded block in thecurrent picture is, for example, a neighboring block of the currentblock.

FIG. 44 is a flow chart illustrating another example of a processperformed by the prediction processor of decoder 200.

The prediction processor determines either a method or a mode forgenerating a prediction image (Step Sr_1). For example, the method ormode may be determined based on, for example, a prediction parameter,etc.

When determining a first method as a mode for generating a predictionimage, the prediction processor generates a prediction image accordingto the first method (Step Sr_2 a). When determining a second method as amode for generating a prediction image, the prediction processorgenerates a prediction image according to the second method (Step Sr_2b). When determining a third method as a mode for generating aprediction image, the prediction processor generates a prediction imageaccording to the third method (Step Sr_2 c).

The first method, the second method, and the third method may bemutually different methods for generating a prediction image. Each ofthe first to third methods may be an inter prediction method, an intraprediction method, or another prediction method. The above-describedreconstructed image may be used in these prediction methods.

Intra Predictor

Intra predictor 216 generates a prediction signal (intra predictionsignal) by performing intra prediction by referring to a block or blocksin the current picture stored in block memory 210, based on the intraprediction mode parsed from the encoded bitstream. More specifically,intra predictor 216 generates an intra prediction signal by performingintra prediction by referring to samples (for example, luma and/orchroma values) of a block or blocks neighboring the current block, andthen outputs the intra prediction signal to prediction controller 220.

It is to be noted that when an intra prediction mode in which a lumablock is referred to in intra prediction of a chroma block is selected,intra predictor 216 may predict the chroma component of the currentblock based on the luma component of the current block.

Moreover, when information parsed from an encoded bitstream indicatesthat PDPC is to be applied, intra predictor 216 corrects intra-predictedpixel values based on horizontal/vertical reference pixel gradients.

Inter Predictor

Inter predictor 218 predicts the current block by referring to areference picture stored in frame memory 214. Inter prediction isperformed in units of a current block or a sub-block (for example, a 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or the sub-block byperforming motion compensation by using motion information (for example,a motion vector) parsed from an encoded bitstream (for example, aprediction parameter output from entropy decoder 202), and outputs theinter prediction signal to prediction controller 220.

It is to be noted that when the information parsed from the encodedbitstream indicates that the OBMC mode is to be applied, inter predictor218 generates the inter prediction signal using motion information of aneighboring block in addition to motion information of the current blockobtained from motion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates that the FRUC mode is to be applied, inter predictor 218derives motion information by performing motion estimation in accordancewith the pattern matching method (bilateral matching or templatematching) parsed from the encoded bitstream. Inter predictor 218 thenperforms motion compensation (prediction) using the derived motioninformation.

Moreover, when the BIO mode is to be applied, inter predictor 218derives a motion vector based on a model assuming uniform linear motion.Moreover, when the information parsed from the encoded bitstreamindicates that the affine motion compensation prediction mode is to beapplied, inter predictor 218 derives a motion vector of each sub-blockbased on motion vectors of neighboring blocks.

MV Derivation > Normal Inter Mode

When information parsed from an encoded bitstream indicates that thenormal inter mode is to be applied, inter predictor 218 derives an MVbased on the information parsed from the encoded bitstream and performsmotion compensation (prediction) using the MV.

FIG. 45 is a flow chart illustrating an example of inter prediction innormal inter mode in decoder 200.

Inter predictor 218 of decoder 200 performs motion compensation for eachblock. Inter predictor 218 obtains a plurality of MV candidates for acurrent block based on information such as MVs of a plurality of decodedblocks temporally or spatially surrounding the current block (StepSs_1). In other words, inter predictor 218 generates an MV candidatelist.

Next, inter predictor 218 extracts N (an integer of 2 or larger) MVcandidates from the plurality of MV candidates obtained in Step Ss_1, asmotion vector predictor candidates (also referred to as MV predictorcandidates) according to a determined priority order (Step Ss_2). It isto be noted that the priority order may be determined in advance foreach of the N MV predictor candidates.

Next, inter predictor 218 decodes motion vector predictor selectioninformation from an input stream (that is, an encoded bitstream), andselects, one MV predictor candidate from the N MV predictor candidatesusing the decoded motion vector predictor selection information, as amotion vector (also referred to as an MV predictor) of the current block(Step Ss_3).

Next, inter predictor 218 decodes an MV difference from the inputstream, and derives an MV for a current block by adding a differencevalue which is the decoded MV difference and a selected motion vectorpredictor (Step Ss_4).

Lastly, inter predictor 218 generates a prediction image for the currentblock by performing motion compensation of the current block using thederived MV and the decoded reference picture (Step Ss_5).

Prediction Controller

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208. As a whole, the configurations, functions, and processesof prediction controller 220, intra predictor 216, and inter predictor218 at the decoder side may correspond to the configurations, functions,and processes of prediction controller 128, intra predictor 124, andinter predictor 126 at the encoder side.

Mounting Example of Decoder

FIG. 46 is a block diagram illustrating a mounting example of decoder200. Decoder 200 includes processor b 1 and memory b 2. For example, theplurality of constituent elements of decoder 200 illustrated in FIG. 41are mounted on processor b 1 and memory b 2 illustrated in FIG. 46 .

Processor b 1 is circuitry which performs information processing and isaccessible to memory b 2. For example, processor b 1 is dedicated orgeneral electronic circuitry which decodes a video (that is, an encodedbitstream). Processor b 1 may be a processor such as a CPU. In addition,processor b 1 may be an aggregate of a plurality of electronic circuits.In addition, for example, processor b 1 may take the roles of two ormore constituent elements out of the plurality of constituent elementsof decoder 200 illustrated in FIG. 41 , etc.

Memory b 2 is dedicated or general memory for storing information thatis used by processor b 1 to decode an encoded bitstream. Memory b 2 maybe electronic circuitry, and may be connected to processor b 1. Inaddition, memory b 2 may be included in processor b 1. In addition,memory b 2 may be an aggregate of a plurality of electronic circuits. Inaddition, memory b 2 may be a magnetic disc, an optical disc, or thelike, or may be represented as a storage, a recording medium, or thelike. In addition, memory b 2 may be a non-volatile memory, or avolatile memory.

For example, memory b 2 may store a video or a bitstream. In addition,memory b 2 may store a program for causing processor b 1 to decode anencoded bitstream.

In addition, for example, memory b 2 may take the roles of two or moreconstituent elements for storing information out of the plurality ofconstituent elements of decoder 200 illustrated in FIG. 41 , etc.Specifically, memory b 2 may take the roles of block memory 210 andframe memory 214 illustrated in FIG. 41 . More specifically, memory b 2may store a reconstructed block, a reconstructed picture, etc.

It is to be noted that, in decoder 200, all of the plurality ofconstituent elements illustrated in FIG. 41 , etc. may not beimplemented, and all the processes described above may not be performed.Part of the constituent elements indicated in FIG. 41 , etc. may beincluded in another device, or part of the processes described above maybe performed by another device.

Definitions of Terms

The respective terms may be defined as indicated below as examples.

A picture is an array of luma samples in monochrome format or an arrayof luma samples and two corresponding arrays of chroma samples in 4:2:0,4:2:2, and 4:4:4 color format. A picture may be either a frame or afield.

A frame is the composition of a top field and a bottom field, wheresample rows 0, 2, 4, ... originate from the top field and sample rows 1,3, 5, ... originate from the bottom field.

A slice is an integer number of coding tree units contained in oneindependent slice segment and all subsequent dependent slice segments(if any) that precede the next independent slice segment (if any) withinthe same access unit.

A tile is a rectangular region of coding tree blocks within a particulartile column and a particular tile row in a picture. A tile may be arectangular region of the frame that is intended to be able to bedecoded and encoded independently, although loop-filtering across tileedges may still be applied.

A block is an M×N (M-column by N-row) array of samples, or an M×N arrayof transform coefficients. A block may be a square or rectangular regionof pixels including one Luma and two Chroma matrices.

A coding tree unit (CTU) may be a coding tree block of luma samples of apicture that has three sample arrays, or two corresponding coding treeblocks of chroma samples. Alternatively, a CTU may be a coding treeblock of samples of one of a monochrome picture and a picture that iscoded using three separate color planes and syntax structures used tocode the samples.

A super block may be a square block of 64×64 pixels that consists ofeither 1 or 2 mode info blocks or is recursively partitioned into four32×32 blocks, which themselves can be further partitioned.

ASPECT 1

Hereinafter, descriptions are given of encoder 100, decoder 200, anencoding method, and a decoding method according to Aspect 1 of thepresent disclosure. Encoder 100 according to Aspect 1 switches methodsof quantization processing on a current block to be encoded (hereinafteralso referred to as a current block to be processed or a current CU tobe processed), according to application or non-application of frequencytransform processing (hereinafter also simply referred to as transformprocessing) such as orthogonal transform and secondary transform.Decoder 200 according to Aspect 1 switches methods of quantizationprocessing on a current block to be decoded (hereinafter also referredto as a current block to be processed or a current CU to be processed),according to application or non-application of inverse frequencytransform processing (hereinafter also simply referred to as inversetransform processing) such as inverse orthogonal transform and inversesecondary transform.

Encoder 100 reduces the overall amount of codes by performing frequencytransform and quantization on prediction errors of a current block to beencoded. The frequency transform is performed using a transform basis.For example, encoder 100 determines a transform basis by selecting froma plurality of transform basis candidates, and performs the frequencytransform using the transform basis determined. Encoder 100 may performre-transform (what is called secondary transform) so that a largernumber of coefficients which are 0 (referred to as zero coefficients)occur sequentially before quantization after frequency transform. Inthis case, the frequency transform is also represented as orthogonaltransform or primary transform. It is to be noted that decoder 200performs an operation corresponding to an operation performed by encoder100.

First, a method of selecting a transform basis in transform processingis described.

A Method of Selecting a Transform Basis in Implicit MTS (IMTS)

Transformer 106 in encoder 100 transforms prediction errors in a spatialdomain into transform coefficients in a frequency domain, and outputsthe transform coefficients to quantizer 108. Specifically, for example,transformer 106 performs predetermined discrete cosine transform (DCT)or discrete sine transform (DST) on the prediction errors in the spatialdomain. Alternatively, transformer 106 may adaptively select a transformtype from among a plurality of transform types, and transform theprediction errors into the transform coefficients using a transformbasis function (hereinafter also referred to as a transform basis or abasis) corresponding to the transform type selected. Such transform maybe referred to as adaptive multiple transform (AMT) or explicit multiplecore transform (EMT). Alternatively, ATM and EMT may be referred to asmultiple transform selection (MTS).

When applying MTS, transformer 106 selects an orthogonal transform basis(also referred to as a primary transform basis) which is for exampleDST-VII or DCT-VIII (see FIG. 5A). The basis selected is to be encodedas index information for each CU.

On the other hand, there is processing such as IMTS as processing ofselecting a basis (what is called an orthogonal transform basis) for usein orthogonal transform based on the shape of a CU without encoding suchindex information. When applying IMTS in an example case where a currentCU has a rectangular shape, transformer 106 performs orthogonaltransform on the short-side portions of the current rectangle CU usingthe transform basis function corresponding to DST-VII (see FIG. 5A), andperforms orthogonal transform on the long-side portions of the currentrectangle CU using the transform basis function corresponding to DCT-II.In an example case where a current CU has a square shape, transformer106 performs orthogonal transform on prediction errors in the squaredomain using the transform basis function corresponding to DCT-II whenMTS is valid in a sequence, and performs orthogonal transform on theprediction errors in the square domain using the transform basisfunction corresponding to DST-VII when MTS is invalid. It is to be notedthat DCT-II and DST-VII are examples, and thus other bases may be used,or the above basis combination may be a different combination. IMTS maybe used only in an intra-prediction block, or may be used in both anintra-prediction block and an inter-prediction block.

Three kinds of processing (hereinafter also referred to as basisselection processing) which are MTS, SBT, and IMTS have been describedabove as methods of selectively switching bases for use in orthogonaltransform. However, all the three kinds of processing may be valid, oronly some kinds of the processing selected from the three kinds ofprocessing may be valid. Whether each of the three kinds of basisselection processing is set to be valid can be identified by, forexample, flag information in a header. The flag information is aSequence Parameter Set (SPS), or the like. For example, when all thethree kinds of basis selection processing are valid, one of the threekinds of basis selection processing is selected and then orthogonaltransform is performed using the basis selection processing selected. Itis only necessary that the processing of selectively switching bases foruse in orthogonal transform provide at least one of the followingfunctions: (1) orthogonal-transforming the entire range in a CU, andencoding information indicating the basis used in the transform; (2)orthogonal-transforming the entire range in a CU, and determining abasis based on a predetermined rule without encoding informationindicating the basis used in the transform; (3) orthogonal-transforminga partial domain of a CU, and encoding information indicating the basisused in the transform; and (4) orthogonal-transforming a partial domainof a CU, and determining a basis based on a predetermined rule withoutencoding information indicating the basis used in the transform.Alternatively, for example, basis selection processing different fromany of the three kinds of processing may be added, or other processingmay replace any of the three kinds of processing.

Although the example processing of selecting the basis for use inorthogonal transform for each unit which is a CU has been describedhere, the unit of processing is not limited to the CU. In other words,whether to apply MTS, SBT, and IMTS may be determined for each unit ofprocessing different from the CU. For example, whether to apply theprocessing may be determined for each unit which is a sequence, apicture, a tile, a slice or a CTU.

It is to be noted that a tool for selectively switching bases for use inorthogonal transform in the present disclosure may be stated differentlyas a method of adaptively selecting a basis for use in transformprocessing (what is called orthogonal transform) or a process forselecting either basis selection processing or a basis. .Alternatively,the tool for selectively switching bases may be stated differently as amode for adaptively selecting a transform basis.

In addition, transformer 106 may perform re-transform (hereinafter alsoreferred to as secondary transform) on transform coefficients obtainedthrough orthogonal transform. Such re-transform may be referred to asnon-separable secondary transform (NSST). For example, transformer 106may perform re-transform for each sub-block (for example, a 4×4sub-block) included in a block of transform coefficients correspondingto intra-prediction errors. Information indicating whether to apply NSSTand information regarding a transform matrix for use in NSST arenormally transformed into signals at a CU level. Hereinafter,transforming information, etc. into signals is also referred to assignaling.

It is to be noted that there is no need to limit to the transform of theinformation into signals that is performed at the CU level, and suchtransform may be performed at another level (for example, at a sequence,picture, slice, tile, or CTU level).

Encoding and Decoding According to Aspect 1

First, encoding according to Aspect 1 of the present disclosure isdescribed. As described above, in the encoding according to Aspect 1,encoder 100 switches quantization processing on a current block to beencoded, according to application or non-application of transformprocessing such as orthogonal transform and secondary transform.

Encoder 100 includes circuitry and memory coupled to the circuitry. Thecircuitry and memory of encoder 100 may correspond to processor a1 andmemory a2 illustrated in FIG. 40 . In operation, the circuitry ofencoder 100 performs the processing indicated below.

Encoder 100 according to Aspect 1 performs quantization on a pluralityof transform coefficients of a current block to be encoded, using aquantization matrix (QM) when orthogonal transform is performed on thecurrent block and secondary transform is not performed on the currentblock; and performs quantization on the plurality of transformcoefficients of the current block without using the quantization matrixwhen orthogonal transform is not performed on the current block and whenboth orthogonal transform and secondary transform are performed on thecurrent block.

In other words, in Aspect 1, encoder 100 determines whether to use aquantization matrix in the quantization processing, based on theinformation for each unit which is the current block to be encodedindicating whether transform processing (what is called orthogonaltransform processing) on the current block has been skipped and whethersecondary transform on the plurality of transform coefficients in thecurrent block has been skipped.

Alternatively, encoder 100 according to Aspect 1 may determine whetherto use a quantization matrix in the quantization processing on thecurrent block, based on information indicating whether orthogonaltransform on the current block has been performed and whether secondarytransform has been performed on the plurality of transform coefficientsin the current block.

Hereinafter, the quantization processing in Aspect 1 is described morespecifically with reference to the drawings. FIG. 47 is a flow chartindicating one example of an operation in the quantization processingperformed by encoder 100 according to Aspect 1.

As described in FIG. 47 , encoder 100 firstly determines whetherorthogonal transform processing on a current block (CU) to be encodedhas been skipped (Step S001).

In the orthogonal transform processing, transformer 106 (see FIG. 1 )may (i) perform predetermined orthogonal transform such as discretecosine transform (DCT) on a CU (more specifically, prediction residualsin the spatial domain of the CU), or (ii) may adaptively select atransform type from among a plurality of transform types, and performorthogonal transform on the CU using a transform basis functioncorresponding to the transform type selected. Alternatively, encoder 100may switch whether to skip orthogonal transform processing on a CU foreach unit that is a block to be processed (that is, for each CU). Atthis time, for example, encoder 100 may encode flag information (forexample, a transform skip flag), or the like for each unit that is theblock (CU), and perform signaling as to whether to perform orthogonaltransform on the CU.

As described in FIG. 47 , in the case where encoder 100 determines thatorthogonal transform processing on the CU has been skipped (Yes in StepS001), that is, when encoder 100 does not perform orthogonal transformon the CU, encoder 100 performs quantization on the CU (morespecifically, the prediction errors in the spatial domain of the CUobtained), without using a quantization matrix (QM) (Step S004).

In the opposite case where encoder 100 determines that orthogonaltransform processing on the CU has not been skipped (No in Step S001),that is, when encoder 100 performs orthogonal transform on the CU,encoder 100 determines whether secondary transform processing on the CUhas been skipped (Step S002). In Aspect 1, encoder 100 may performorthogonal transform such as DCT, and then perform secondary transformon coefficient values in the orthogonal transform. For example, thesecondary transform may be NSST.

In the case where encoder 100 determines that secondary transformprocessing on the CU has not been skipped (No in Step S002), in otherwords, when encoder 100 performs secondary transform on a plurality oftransform coefficients of the CU, encoder 100 performs quantization onthe CU without using the quantization matrix (QM) (Step S004). Thecoefficient distribution after the secondary transform is different fromthe coefficient distribution in the orthogonal transform such as DCT.Thus, the CU to which secondary transform has been applied may bequantized without using the QM. The quantization processing performedwithout using the QM may be processing of quantizing transformcoefficients based on a quantization width which can be calculated basedon a quantization parameter. It is to be noted that, in the quantizationprocessing performed without using the QM, a predetermined value commonto all the secondary transform coefficients in a block may be multipliedto the quantization width.

In the opposite case where encoder 100 determines that secondarytransform processing on the CU has been skipped (Yes in Step S002), inother words, encoder 100 does not perform secondary transform on the CU,encoder 100 performs quantization on the CU (more specifically, aplurality of transform coefficients in the CU obtained) using aquantization matrix (QM) (Step S003). When using the QM, for example,encoder 100 performs, using a value in the QM for each transformcoefficient, scaling of the quantization width, or the like which can becalculated based on a quantization parameter, or the like.

It is to be noted that encoder 100 may switch whether to validateskipping of transform processing (that is, orthogonal transformprocessing and secondary transform processing), according to the size ofa current block (CU). For example, encoder 100 always invalidatesskipping of transform processing on a current block whose short-sidelength exceeds 32.

It is to be noted that, in intra prediction, encoder 100 may split acurrent block into a plurality of sub-partitions, and sequentiallyperform intra prediction for each sub-partition by referring to aprediction image or a reconstructed image of an encoded sub-partition inthe current block (this is referred to as an intra sub-partition mode).In the encoding of the current block to which such intra sub-partitionmode has been applied, quantization processing is performed for eachsub-partition. Also in this case, encoder 100 is capable of specifyingwhether to skip transform processing for each unit that is a currentblock (for each CU). For example, when orthogonal transform processingon the current block has been skipped, encoder 100 may performquantization processing on all the sub-partitions in the current blockwithout using the QM.

It is to be noted that encoder 100 may directly encode pixel values of acurrent image to be encoded according to an approach such asdifferential pulse-code modulation (DPCM), without performing anyprediction processing. In other words, also when the pixel values of thecurrent block have been encoded according to the approach such as DPCM,encoder 100 may perform quantization processing on the CU without usingthe QM.

Here, it is only necessary that the current block be a unit ofprocessing including a plurality of pixels, and thus the current blockmay be a unit of processing including a plurality of CUs.

A QM provides an effect of adjusting a subjective image quality byscaling a quantization width, or the like of coefficients in the domainafter being subjected to transform such as orthogonal transform. Thus,there is a possibility that a sufficient effect is not obtained even ifa QM is applied when transform processing has been skipped. Accordingly,there is a possibility that decrease in subjective image quality can bereduced by performing quantization processing without using any QM whentransform processing on a block has been skipped in the encoding inAspect 1.

This processing flow is one example, and thus it is to be noted that theprocessing order described may be changed, part of the processing may beremoved, and processing which is not described may be added. Forexample, the encoding in Aspect 1 may be applied to encoding accordingto Aspect 2, Aspect 3, or Aspect 4 to be described later. These aspectsrelate to encoding of rectangular blocks. Furthermore, the encoding inAspect 1 may be applied to encoding of blocks having a shape other thana rectangular shape.

Next, decoding according to Aspect 1 is described. As described above,in the decoding according to Aspect 1, inverse quantization processingis switched for a current block to be decoded, according to applicationor non-application of inverse transform processing such as inverseorthogonal transform and inverse secondary transform on the currentblock.

Decoder 200 includes circuitry and memory coupled to the circuitry. Thecircuitry and memory of decoder 200 may correspond to processor b 1 andmemory b 2 illustrated in FIG. 46 . In operation, the circuitry ofdecoder 200 performs the processing indicated below.

Decoder 200 according to Aspect 1 performs inverse quantization on aplurality of transform coefficients of a current block to be decoded,using a quantization matrix (QM) when inverse orthogonal transform isperformed on the current block and inverse secondary transform is notperformed on the current block; and performs inverse quantization on theplurality of transform coefficients of the current block without usingthe quantization matrix when inverse orthogonal transform is notperformed on the current block and when both inverse orthogonaltransform and inverse secondary transform are performed on the currentblock.

In other words, in Aspect 1, decoder 200 determines whether to use thequantization matrix in the inverse quantization processing, based on theinformation for each unit which is the current block to be decodedindicating whether inverse transform processing (what is called inverseorthogonal transform processing) on the current block has been skippedand whether inverse secondary transform processing on the current blockhas been skipped.

Alternatively, decoder 200 according to Aspect 1 may determine whetherto use a quantization matrix in the inverse quantization processing onthe current block, based on information indicating whether inverseorthogonal transform on the current block has been performed and whetherinverse secondary transform on a plurality of transform coefficients inthe current block has been performed.

Hereinafter, the inverse quantization processing in Aspect 1 isdescribed more specifically with reference to the drawings. FIG. 48 is aflow chart indicating one example of an operation in the inversequantization processing performed by decoder 200 according to Aspect 1.

As described in FIG. 48 , decoder 200 firstly determines whether inverseorthogonal transform processing on a current block (CU) to be decoded isskipped (Step S011).

In the inverse transform processing, inverse transformer 206 (see FIG.41 ) restores prediction errors by inverse-transforming transformcoefficients which are input from inverse quantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when an AMT flag is true),inverse transformer 206 inverse-transforms the transform coefficients ofthe current block based on the information indicating the transform typeparsed. As another example, when information parsed from an encodedbitstream indicates application of NSST, inverse transformer 206 appliesinverse transform to the transformed coefficients.

Alternatively, decoder 200 may switch whether to skip inverse orthogonaltransform processing on a CU for each unit of a block to be processed(that is, for each CU). At this time, for example, decoder 200 maydecode flag information (for example, an inverse transform skip flag)for each unit of processing that is a current block (CU) to beprocessed, and parse whether inverse orthogonal transform is performedon the CU.

In the decoding, decoder 200 determines whether prediction residualshave been transformed, based on the flag information described above. Itis to be noted that whether to validate skipping of inverse transformmay be identified based on identification information included in headerinformation in an SPS, a PPS, or the like.

As illustrated in FIG. 48 , in the case where decoder 200 determinesthat inverse orthogonal transform processing on the CU is skipped (Yesin Step S011), in other words, when decoder 200 does not perform inverseorthogonal transform on the CU, decoder 200 performs inversequantization on the CU (more specifically, a plurality of quantizedcoefficients in the CU) without using a quantization matrix (QM) (StepS014).

In the inverse quantization processing, inverse quantizer 204 of decoder200 (see FIG. 41 ) inverse-quantizes quantized coefficients of thecurrent block which are input from entropy decoder 202 (see FIG. 41 ).Specifically, inverse quantizer 204 inverse-quantizes each of thequantized coefficients of the current block, based on a quantizationparameter corresponding to the quantized coefficient. Subsequently,inverse quantizer 204 outputs, to inverse transformer 206, the quantizedcoefficients (that are transform coefficients) which have beeninverse-quantized of the current block (see FIG. 41 ).

In the opposite case where decoder 200 determines that inverseorthogonal transform processing on the CU is not skipped (No in StepS011), in other words, when decoder 200 performs inverse orthogonaltransform on the CU, decoder 200 determines whether inverse secondarytransform processing on the CU is skipped (Step S012). For example, wheninformation parsed from an encoded bitstream indicates that secondarytransform processing (for example, NSST) is applied, decoder 200determines that inverse secondary transform processing on the CU isperformed.

In the case where decoder 200 determines that inverse secondarytransform processing on the CU is not skipped (No in Step S012), thatis, when decoder 200 performs inverse secondary transform on a pluralityof secondary transform coefficients in the CU, decoder 200 performsinverse quantization on the CU without using the quantization matrix(QM) (Step S014).

In the opposite case where decoder 200 determines that inverse secondarytransform processing on the CU is skipped (Yes in Step S012), that is,when decoder 200 does not perform inverse secondary transform on the CU,decoder 200 performs inverse quantization on the CU (more specifically,a plurality of quantized coefficients in the CU) using a quantizationmatrix (QM) (Step S013).

It is to be noted that decoder 200 may switch whether to validateskipping of the inverse transform processing (that is the inverseorthogonal transform processing and the inverse secondary transformprocessing described above) according to the size of the current block(CU). For example, decoder 200 always invalidates skipping of theinverse transform processing in a current block whose short-side lengthexceeds 32.

It is to be noted that, in intra prediction, encoder 100 may split acurrent block into a plurality of sub-partitions, and sequentiallyperform intra prediction for each sub-partition by referring to aprediction image or a reconstructed image of a decoded sub-partition(this is referred to as an intra sub-partition mode). In the decoding ofthe current block to which such intra sub-partition mode has beenapplied, inverse quantization processing is performed for eachsub-partition. Also in this case, decoder 200 is capable of specifyingwhether to skip inverse transform processing for each unit that is acurrent block (for each CU). For example, when inverse orthogonaltransform processing on the current block has been skipped, decoder 200may perform inverse quantization processing on all the sub-partitions inthe current block without using the QM.

Here, it is only necessary that the current block be a unit ofprocessing including a plurality of pixels, and thus the current blockmay be a unit of processing including a plurality of CUs.

Accordingly, there is a possibility that decrease in subjective imagequality can be reduced by performing inverse quantization processingwithout using the QM when inverse transform processing on a block hasbeen skipped in the decoding in Aspect 1.

This processing flow is one example, and thus it is to be noted that theprocessing order described may be changed, part of the processing may beremoved, and processing which is not described may be added.Alternatively, for example, the decoding according to Aspect 1 may beapplied to Aspect 2, Aspect 3, or Aspect 4 to be described later. Theseaspects relate to decoding of rectangular blocks. Furthermore, thedecoding according to Aspect 1 may be applied to decoding of blockshaving a shape other than a rectangular shape.

Effects of Aspect 1 Relating to Encoding and Decoding

As described above, a quantization matrix provides an effect ofadjusting a subjective image quality by scaling a quantization width, orthe like of coefficients in a domain after transform such as orthogonaltransform. Thus, there is a possibility that a sufficient effect is notobtained even if a quantization matrix is applied to predictionresiduals of a plurality of pixel value in a current block to beencoded, when no orthogonal transform on the current block is performed.In addition, when orthogonal transform and secondary transform areperformed on the current block, since a plurality of transformcoefficients in the current block after the orthogonal transform hasbeen re-transformed, there is a possibility that a sufficient effect isnot obtained even if a quantization matrix is applied to thecoefficients re-transformed. For this reason, encoder 100 according toAspect 1 of the present disclosure configured as described withreference to FIG. 47 performs quantization on the current block to beencoded which may not provide a sufficient effect of adjusting thesubjective image quality even if the quantization matrix is appliedthereto, without using the quantization matrix, which reduces theprocessing amount. Furthermore, encoder 100 according to Aspect 1 of thepresent disclosure is capable of appropriately applying the quantizationmatrix to the plurality of prediction residuals in the current blockafter orthogonal transform has been performed thereon, which provides aneffect of adjusting the subjective image quality. Accordingly, encoder100 according to Aspect 1 of the present disclosure is capable ofappropriately determining whether to use the quantization matrix for thecurrent block in the quantization processing, which makes it possible toincrease the coding efficiency while reducing decrease in subjectiveimage quality both in a case in which the quantization matrix is appliedand in a case of the quantization matrix is not applied.

Furthermore, decoder 200 according to Aspect 1 of the present disclosureconfigured as described with reference to FIG. 48 performs inversequantization, without using the quantization matrix, on a current blockto be decoded which may not provide a sufficient effect of adjusting asubjective image quality even if a quantization matrix is appliedthereto, which reduces the processing amount. Furthermore, decoder 200according to Aspect 1 of the present disclosure is capable ofappropriately applying the quantization matrix to the current blockafter orthogonal transform and quantization have been performed thereon,which provides an effect of adjusting the subjective image quality.Accordingly, decoder 200 according to Aspect 1 of the present disclosureis capable of appropriately determining whether to use the quantizationmatrix for the current block in the inverse quantization processing,which makes it possible to increase the processing efficiency whilereducing decrease in subjective image quality both in the case in whichthe quantization matrix is applied and in the case of the quantizationmatrix is not applied.

A Variation of Aspect 1 Relating to Encoding and Decoding

In the encoding and decoding according to Aspect 1, the followingprocessing may be applied.

For example, information indicating whether to validate scaling using aquantization matrix (QM) may be indicated by flag information includedin header information in an SPS, a PPS, or the like.

Alternatively, whether to validate skipping of transform processing andskipping of inverse transform processing may be determined according tothe size of a current block to be encoded and the size of a currentblock to be decoded, respectively. Hereinafter, the current block to beencoded and the current block to be decoded are also collectivelyreferred to as current blocks to be processed. For example, skipping oftransform processing and inverse transform processing may be alwaysinvalidated for the current blocks to be processed each having apredetermined size or more.

Alternatively, whether to validate skipping of transform processing andinverse transform processing may be set based on conditions differentbetween luminance signals and chrominance signals in the current blockto be processed. For example, skipping of transform processing andinverse transform processing may be applied only to the luminancesignals. At this time, for the luminance signals, whether to performscaling using a QM may be determined based on information indicatingwhether to apply skipping of transform processing and inverse transformprocessing on the current blocks to be processed. At this time, sinceskipping of transform processing and inverse transform processing on thechrominance signals are always invalidated, scaling using the QM isperformed regardless of whether to apply transform processing andinverse transform processing to the current blocks (in other words,whether the skipping is valid or invalid). Alternatively, it isexcellent that skipping of transform processing and inverse transformprocessing may be applicable to both the luminance signals and thechrominance signals. At this time, signaling regarding skipping oftransform processing and inverse transform processing on the luminancesignals and the chrominance signals may be made common by, for example,validating skipping of transform processing and inverse transformprocessing on the chrominance signals of the current blocks to beprocessed when skipping of transform processing and inverse transformprocessing on the luminance signals of the current blocks is valid. Inaddition, signaling regarding the luminance signals and signalingregarding the chrominance signals may be performed separately. At thistime, for example, it is possible to perform control such as control tovalidate skipping of transform processing and inverse transformprocessing on the luminance signals, and to invalidate skipping oftransform processing and inverse transform processing on the chrominancesignals. When signaling regarding skipping of transform processing onluminance signals and signaling regarding skipping chrominance signalsare common, whether to perform scaling using a QM may be determinedbased on common signaling information. On the other hand, when signalingregarding luminance signals and signaling regarding chrominance signalsare performed separately, skipping of transform processing on theluminance signals and skipping of transform processing on thechrominance signals may be applied separately based on the signalinginformation regarding the luminance signals and the signalinginformation regarding the chrominance signals, respectively. Forexample, when transform processing on the luminance signals is skipped,control may be performed so as not to perform scaling using a QM on theluminance signals.

As described above, encoder 100 is capable of directly encoding pixelvalues of a current image to be encoded according to an approach that isfor example differential pule-code modulation (DPCM) or pulse-codemodulation (PCM), without performing transform processing as describedabove. At this time, encoder 100 may directly encode residual signalsbetween an original image and a prediction image after performingprediction processing, instead of directly encoding the pixel values ofthe current image to be encoded. In addition, encoder 100 may allowselection on whether to quantize signals which have been directlyencoded. At this time, encoder 100 may apply scaling using a QM whenquantizing signals which have been directly encoded, or may alwaysinvalidate scaling using the QM when not quantizing signals which havebeen directly encoded. Alternatively, encoder 100 may always invalidatescaling using a QM even when quantizing signals which have been directlyencoded. Furthermore, encoder 100 may use either a QM for intraprediction and a QM for inter prediction when quantizing signals whichhave been directly encoded, or may set a unique QM and encode the uniqueQM in an SPS header or a PPS header.

It is to be noted that the above-described processing may be applied toencoding and decoding in each of Aspect 1 to Aspect 4.

ASPECT 2

Hereinafter, descriptions are given of encoder 100, decoder 200, anencoding method, and a decoding method according to Aspect 2 of thepresent disclosure.

In the encoding according to Aspect 1, quantization processing isswitched according to application or non-application of transformprocessing on the current block to be encoded. In Aspect 2, a QM for arectangular block is generated based on a QM for a square block when acurrent block to be encoded has a rectangular shape, and thenquantization processing is performed on the current block using the QM.

When the current block is the rectangular block, encoder 100 accordingto Aspect 2 of the present disclosure may generate a second quantizationmatrix corresponding to a plurality of transform coefficients of therectangular block by transforming a first quantization matrixcorresponding to a plurality of transform coefficients of a squareblock, and quantize the plurality of transform coefficients of therectangular block using the second quantization matrix.

Hereinafter, encoding including the quantization processing according toAspect 2 is described more specifically with reference to the drawings.

Encoding and Decoding According to Aspect 2

FIG. 49 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in encoder 100 according to Aspect 2.It is to be noted that encoder 100 described here performs encoding foreach square or rectangular block obtained by splitting a picture(hereinafter also referred to as a frame) included in a video.

First, in Step S101, quantizer 108 generates a QM for a square block.The QM for the square block is a quantization matrix corresponding to aplurality of transform coefficients of a square block. Hereinafter, theQM for the square block is also referred to as a first quantizationmatrix. It is to be noted that quantizer 108 may generate the QM for thesquare block based on values which have been defined by a user andpre-set in encoder 100, or may adaptively generate the QM for the squareblock using encoded information of a picture which has been alreadyencoded. In addition, entropy encoder 110 may describe, in a stream, asignal relating to the QM (that is, a QM signal) for the square blockgenerated by quantizer 108. At this time, the QM for the square blockmay be encoded in an area in the stream. The area is one of a sequenceheader area, a picture header area, a slice header area, a supplementalinformation area, or another area storing another parameter. It is to benoted that the QM for the square block does not always need to bedescribed in a stream. At this time, quantizer 108 may use defaultvalues in a QM for the square block that is a QM which has beenpre-defined in a standard. Alternatively, entropy encoder 110 maydescribe, in the stream, only a part of coefficients required togenerate the QM, instead of describing, in the stream, all thecoefficients (that are quantized coefficients) in the QM for the squareblock. In this way, it is possible to reduce the amount of informationto be encoded.

Next, in Step S102, quantizer 108 generates a QM for a rectangular blockusing the QM for the square block generated in Step S101. Hereinafter,the QM for the rectangular block is also referred to as a secondquantization matrix. It is to be noted that entropy encoder 110 does notdescribe a QM signal for a rectangular block in the stream.

It is to be noted, as explained with reference to FIG. 49 , that each ofthe processing in Step S101 and the processing in Step S102 may beperformed on the blocks collectively at the time of starting processingof a sequence, a picture, or a slice, or may be performed each time whenpart of the processing is performed in processing of a unit that is ablock. In addition, the QMs which are generated by quantizer 108 in StepS101 and Step S102 may be a plurality of kinds of QMs for blocks havingthe same block size which are generated by splitting a block, underconditions such as whether each QM is for a luminance block or for achrominance block, each QM is for an intra-prediction block or for aninter-prediction block, and under other conditions.

Next, a block-based loop is started. First, in Step S103, one of intrapredictor 124 and inter predictor 126 performs, for each block,prediction processing using a corresponding one of intra prediction andinter prediction. In Step S104, transformer 106 performs transformprocessing using discrete cosine transform (DCT), or the like on agenerated prediction residual image. In Step S105, quantizer 108performs quantization on generated transform coefficients using the QMfor the square block and the QM for the rectangular block which areoutputs in Step S101 and Step S102. It is to be noted that, in interprediction, a mode for referring to a block in a picture to which acurrent block to be processed belongs may be used together with a modefor referring to a block in a picture different from a picture to whichthe current block belongs. At this time, the QM for inter prediction maybe used commonly for both the modes, or the QM for intra prediction maybe used to the mode for referring to the block in the picture to whichthe current block belongs. Furthermore, in Step S106, inverse quantizer112 performs inverse quantization on quantized transform coefficientsusing the QM for the square block and the QM for the rectangular blockwhich are outputs in Step S101 and Step S102. In Step S107, inversetransformer 114 performs inverse transform on the transform coefficientson which the inverse quantization has been performed to generate aresidual (prediction error) image. Next, in Step S108, adder 116 addsthe residual image and the prediction image to generate a reconstructedimage. This sequential processing flow is repeated, and block-basedloops end.

In this way, also in the encoding scheme for pictures includingrectangular blocks which have various shapes, describing only QMscorresponding to square blocks in the stream enables encoding withoutdescribing QMs corresponding to the rectangular blocks having variousshapes. In other words, encoder 100 according to Aspect 2 of the presentdisclosure does not require that the QMs corresponding to therectangular blocks are described in the stream, which enables reductionin amount of codes of the header area. Furthermore, encoder 100according to Aspect 2 of the present disclosure is capable of generatingthe QMs corresponding to the rectangular blocks based on the QMscorresponding to the square blocks, which makes it possible to useappropriate QMs also for the rectangular blocks without increasing theamount of codes of the header area. Thus, since encoder 100 according toAspect 2 of the present disclosure is capable of efficiently quantizingthe rectangular blocks having various shapes, which increases thepossibility of being able to increase the coding efficiency. It is to benoted that the QMs for the square blocks do not necessarily need to bedescribed in the stream, and default values in QMs for square blockswhich have been pre-defined in a standard may be used.

It is to be noted that this processing flow is one example, and thus itis to be noted that the processing order described may be changed, partof the processing may be removed, and processing which is not describedmay be added.

Next, decoding according to Aspect 2 is described. In the decodingaccording to Aspect 1, inverse quantization processing is switchedaccording to application or non-application of inverse transformprocessing on the current block to be decoded. In Aspect 2, a QM for arectangular block is generated based on a QM for a square block when acurrent block to be decoded has a rectangular shape, and then inversequantization processing on the current block is performed using the QM.

When the current block is a rectangular block, decoder 200 according toAspect 2 may generate a second quantization matrix corresponding to aplurality of transform coefficients of the rectangular block byconverting a first quantization matrix corresponding to a plurality oftransform coefficients of a square block, and performs inversequantization on the plurality of the transform coefficients of therectangular block using the second quantization matrix.

Hereinafter, the inverse quantization processing according to Aspect 2is described more specifically with reference to the drawings.

FIG. 50 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in decoder 200 according to Aspect 2.It is to be noted that decoder 200 described here performs decoding foreach square or rectangular block obtained by splitting a frame.

First, in Step S201, entropy decoder 202 decodes a signal relating tothe QM for the square block from a stream, and generates the QM for thesquare block using the decoded signal relating to the QM for the squareblock. It is to be noted that the QM for the square block may be decodedfrom an area in the stream. The area is one of a sequence header area, apicture header area, a slice header area, a supplemental informationarea, or another area storing another parameter. Alternatively, the QMfor the square block does not always need to be decoded from the stream.At this time, default values which have been pre-defined in a standardmay be used as values of the QM for the square block. Alternatively,entropy decoder 202 may generate the QM for the square block bydecoding, from the stream, only a part of coefficients required togenerate the QM for the square block, instead of decoding, from thestream, all the coefficients in the QM for the square block.

Next, in Step S202, entropy decoder 202 generates a QM for a rectangularblock using the QM for the square block generated in Step S201. It is tobe noted that entropy decoder 202 does not decode a QM signal for therectangular block from the stream.

It is to be noted that, as explained with reference to FIG. 50 , each ofthe processing in Step S201 and the processing in Step S202 may beperformed on the blocks collectively at the time of starting processingof a sequence, a picture, or a slice, or performed each time when partof the processing is performed in processing of a unit that is a block.In addition, the QMs which are generated by entropy decoder 202 in StepS201 and Step S202 may be a plurality of kinds of QMs for blocks havingthe same block size which are generated under conditions such as whethereach QM is for a luminance block or for a chrominance block, each QM isfor an intra-prediction block or for an inter-prediction block, andunder other conditions.

Next, a block-based loop is started. First, in Step S203, one of intrapredictor 216 and inter predictor 218 performs, for each block,prediction processing using a corresponding one of intra prediction andinter prediction. In Step S204, inverse quantizer 204 performs inversequantization on quantized transform coefficients (that are quantizedcoefficients) decoded from a stream using the QM for the square blockand the QM for the rectangular block which are outputs in Step S201 andStep S202. It is to be noted that, in intra prediction and interprediction, a mode for referring to a block in a picture to which acurrent block to be processed belongs may be used together with a modefor referring to a block in a picture different from a picture to whichthe current block belongs. At this time, the QM for inter prediction maybe used commonly for both the modes, or the QM for intra prediction maybe used in the mode for referring to the block in the picture to whichthe current block belongs. Next, in Step S205, inverse transformer 206performs inverse transform on the inverse-quantized transformcoefficients to generate a residual (prediction error) image. Next, inStep S206, adder 208 adds the residual image and a prediction image togenerate a reconstructed image. This sequential processing flow isrepeated, and block-based loops end.

In this way, also in the encoding scheme for pictures includingrectangular blocks which have various shapes, decoding is possible whenonly QMs corresponding to square blocks have been described in thestream in the encoding scheme even if QMs corresponding to therectangular blocks having various shapes have not been described in thestream. In other words, decoder 200 according to Aspect 2 of the presentdisclosure does not describe the QMs for the rectangular blocks in thestream, which enables reduction in amount of codes of the header area.Furthermore, decoder 200 according to Aspect 2 of the present disclosureis capable of generating the QMs corresponding to the rectangular blocksbased on the QMs corresponding to the square blocks, which makes itpossible to use QMs also for the rectangular blocks without increasingthe amount of codes of the header area. Thus, decoder 200 according toAspect 2 of the present disclosure is capable of efficiently quantizingthe rectangular blocks having various shapes, which increases thepossibility of being able to increase the coding efficiency. It is to benoted that the QMs for the square blocks do not always need to bedescribed in the stream, and default QMs for square blocks which havebeen pre-defined in a standard may be used.

This processing flow is one example, and thus it is to be noted that theprocessing order described may be changed, part of the processing may beremoved, and processing which is not described may be added.

A First Example of a Method of Generating a QM for a Rectangular Blockin Aspect 2

FIG. 51 is a diagram for explaining a first example of generating a QMfor a rectangular block based on a QM for a square block in Step S102 inFIG. 49 and in Step S202 in FIG. 50 . It is to be noted that theprocessing described here is common between encoder 100 and decoder 200.

FIG. 51 indicates, for each of square blocks each having a size in arange from 2×2 to 256×256, the size of a QM for the square block and thesize of a QM for a rectangular block which is generated based on the QMfor the square block in association with each other. The exampleillustrated in FIG. 51 is characterized in that the length of a longside of each rectangular block is the same as the length of one side ofthe corresponding square block. In other words, this example ischaracterized in that the size of a current rectangular block to beprocessed is smaller than the size of the corresponding square block. Inother words, encoder 100 and decoder 200 according to Aspect 1 of thepresent disclosure generates the QM for the rectangular block bydown-converting the QM for the square block having the one side whoselength is the same as the length of the long side of the currentrectangular block to be processed.

It is to be noted that FIG. 51 indicates the correlation relationshipsbetween the QMs for the square blocks which have various block sizes andthe QMs for the rectangular blocks which are generated based on the QMsfor the square blocks without discriminating luminance blocks andchrominance blocks. The correlation relationship between a QM for asquare block and a QM for a rectangular block adapted to a format to beactually used may be derived appropriately. For example, in the case ofa 4:2:0 format, a luminance block has a size that is twice the size of achrominance block. Thus, when referring to the luminance block in theprocessing of generating a QM for a rectangular block based on a QM fora square block, an available QM for the square block corresponds to asquare block having a size in a range from 4×4 to 256×256. At this time,only a QM corresponding to a rectangular block having a size defined bya short-side length of 4 or more and a long-side length of 256 or lessis used as the QM for the rectangular block that is generated based onthe QM for the square block. Thus, when referring to the chrominanceblock in the processing of generating a QM for a rectangular block basedon a QM for a square block, an available QM for the square blockcorresponds to a square block having a size in a range from 2×2 to128×128. At this time, only a QM corresponding to a rectangular blockhaving a size defined by a short-side length of 2 or more and along-side length of 128 or less is used as the QM for the rectangularblock that is generated based on the QM for the square block.

In addition, in the case of a 4:4:4 format for example, a luminanceblock has the same size as the size of a chrominance block. Thus, whenreferring to the chrominance block in the processing of generating a QMfor a rectangular block as in the case of referring to the luminanceblock, an available QM for a square block corresponds to a square blockhaving a size in a range from 4×4 to 256×256.

In this way, the correlation relationship between the QM for the squareblock and the QM for the rectangular block may be appropriately derivedaccording to the format to be actually used.

It is to be noted that the block sizes indicated in FIG. 51 areexamples, and thus block sizes are not limited to the sizes therein. Forexample, QMs which have block sizes other than the block sizes indicatedas examples in FIG. 51 may be used, and only QMs for square blocks eachhaving one of the block sizes indicated in FIG. 51 may be used.

FIG. 52 is a diagram for illustrating a method of generating a QM for arectangular block explained with reference to FIG. 51 by down-convertinga corresponding QM for a square block.

In the example of FIG. 52 , a QM for an 8×4 rectangular block isgenerated based on a QM for an 8×8 square block.

In the down-conversion processing: matrix elements in a QM for a squareblock may be split into groups whose number may be the same as thenumber of matrix elements in a QM for a rectangular block; for each ofthe groups, matrix elements included in the group may be arrangedsequentially in either the horizontal direction or the verticaldirection of the square block; for each of the groups, the matrixelement located at the lowest-frequency side among the matrix elementsin the group may be determined to correspond to one of the matrixelements in the QM for the rectangular block.

For example, in FIG. 52 , the matrix elements in the QM for the 8×8square block are enclosed by bold lines for each predetermined number ofmatrix elements. Each of the predetermined number of matrix elementsenclosed by the bold lines makes up a corresponding one of the groups.In the down-conversion processing illustrated as an example in FIG. 52 ,the QM for the 8×8 square block is split in such a manner that thenumber of the groups is the same as the number of the matrix elements(also referred to as quantized coefficients) in the QM for therectangular block to be generated based on the QM for the 8×8 squareblock. In the example in FIG. 52 , each pair of quantized coefficientsneighboring vertically makes up one of the groups. Next, in the QM forthe 8×8 square block, the quantized coefficient located at thelowest-frequency side (corresponding to the upper side in the example inFIG. 52 ) in each of the groups is selected, and determined to be one ofthe values in the QM for the 8×4 rectangular block.

It is to be noted that the method of selecting one quantized coefficientin each group as a value in the QM for the rectangular block is notlimited to the above example, and another method may be used. Forexample, it is also excellent that, instead of the quantized coefficientlocated at the lowest-frequency side in each group, the quantizedcoefficient located at the highest-frequency side may be handled as oneof the values in the QM for the rectangular block, or the quantizedcoefficient located at a middle-frequency side may be handled as one ofthe values in the QM for the rectangular block. Alternatively, it isalso excellent to use any of the average value, the smallest value, thelargest value, the median value, or the like of all or a part thequantized coefficients in the group, etc. When a decimal value isobtained as a result of calculation of any of these values, it is to benoted that the decimal value may be rounded into an integer value usingrounding-up, rounding-down, rounding-off, or the like.

It is to be noted that methods of selecting one quantized coefficientfrom each of the groups in a QM for a square block may be switchedaccording to a frequency domain in which the group is located in the QMfor the square block. For example, the quantized coefficient located atthe lowest-frequency side in each of the groups located at alow-frequency side may be selected from among the quantized coefficientsin each group; the quantized coefficient located at thehighest-frequency side in each of the groups located at a high-frequencyside may be selected from among the quantized coefficients in eachgroup; and the quantized coefficient located at the middle side in eachof the groups located at an intermediate-frequency side may be selectedfrom among the quantized coefficients in each group.

It is to be noted that, for example, the lowest-frequency component(corresponding to the upper-left quantized coefficient in the example inFIG. 52 ) in a QM for a rectangular block to be generated may bedescribed in a stream and may be directly set from the stream, insteadof deriving a QM for a square block. In that case, the amount ofinformation to be described in the stream increases, and thus the amountof codes of the header area inevitably increases. However, it ispossible to directly control the quantized coefficient of thelowest-frequency component which affects a resulting image quality mostsignificantly in the QM, which increases the possibility of being ableto increase the image quality.

Although the example in the case of generating the QM for therectangular block by vertically down-converting the QM for the squareblock has been described here, it is to be noted that a QM for arectangular block may also be generated by horizontally down-convertinga QM for a square block using a method similar to the method in theexample in FIG. 52 .

A Second Example of a Method of Generating a QM for a Rectangular Blockin Aspect 2

FIG. 53 is a diagram for explaining a second example of generating a QMfor a rectangular block based on a QM for a square block in Step S102 inFIG. 49 and in Step S202 in FIG. 50 . It is to be noted that theprocessing described here is common between encoder 100 and decoder 200.

FIG. 53 indicates, for each of square blocks each having a size in arange from 2×2 to 256×256, the size of a QM for the square block and thesize of a QM for a rectangular block generated based on the QM for thesquare block in association with each other. The example illustrated inFIG. 53 is characterized in that the length of a short side of eachrectangular block is the same as the length of one side of thecorresponding square block. In other words, this example ischaracterized in that the size of the current rectangular block to beprocessed is larger than the size of the corresponding square block. Inother words, encoder 100 and decoder 200 according to Aspect 1 of thepresent disclosure generates the QM for the rectangular block byup-converting the QM for the square block having the one side whoselength is the same as the length of the short side of the currentrectangular block to be processed.

It is to be noted that FIG. 53 indicates the correlation relationshipbetween the QMs for the square blocks which have various block sizes andthe QMs for the rectangular blocks which are generated based on the QMsfor the square blocks without discriminating luminance blocks andchrominance blocks. The correlation relationship between a QM for asquare block and a QM for a rectangular block adapted to a format to beactually used may be derived appropriately. For example, in the case ofa 4:2:0 format, when referring to a luminance block in the processing ofgenerating a QM for a rectangular block based on a QM for a squareblock, only a QM corresponding to a rectangular block having a sizedefined by a short-side length of 4 or more and a long-side length of256 or less is used as the QM for the rectangular block that isgenerated based on the QM for the square block. In addition, whenreferring to a chrominance block in the processing of generating a QMfor a rectangular block based on a QM for a square block, only a QMcorresponding to a rectangular block having a size defined by ashort-side length of 2 or more and a long-side length of 128 or less isused as the QM for the rectangular block that is generated based on theQM for the square block. It is to be noted that the same detailsexplained with reference to FIG. 51 apply to the case of a 4:4:4 format,and thus the same explanation is not repeated here.

In this way, the correlation relationship between the QM for the squareblock and the QM for the rectangular block may be appropriately derivedaccording to the format to be actually used.

It is to be noted that the block sizes indicated in FIG. 53 areexamples, and thus block sizes are not limited to the sizes therein. Forexample, QMs which have block sizes other than the block sizes indicatedas examples in FIG. 53 may be used, and only QMs for square blocks eachhaving one of the block sizes indicated in FIG. 53 may be used.

FIG. 54 is a diagram for illustrating a method of generating each QM fora rectangular block explained with reference to FIG. 53 by up-convertinga corresponding QM for a square block.

In the example of FIG. 54 , the QM for the 8×4 rectangular block basedon the QM for the 4×4 square block.

In the up-conversion processing: (i) matrix elements in a QM for arectangular block may be split into groups whose number may be the sameas the number of matrix elements in a QM for a square block; and foreach of the groups, matrix elements, corresponding to the group, in theQM for the rectangular block may be determined in such a manner thatmatrix elements included in the group are duplicated; or (ii) for eachof the groups, matrix elements, corresponding to the group, in the QMfor the rectangular block may be determined by performing linearinterpolation between neighboring matrix elements among the matrixelements in the QM for the rectangular block.

For example, in FIG. 54 , the matrix elements in the QM for the 8×4rectangular block are enclosed by bold lines for each predeterminednumber of matrix elements. Each of the predetermined number of matrixelements enclosed by the bold lines makes up a corresponding one of thegroups. In the up-conversion processing illustrated as an example inFIG. 54 , the QM for the 8×4 rectangular block is split in such a mannerthat the number of the groups is the same as the number of the matrixelements (also referred to as quantized coefficients) in the QM for the4×4 square block. In the example in FIG. 54 , each pair of quantizedcoefficients neighboring horizontally makes up one of the groups. Next,in the QM for the 8×4 rectangular block, values of the QM for the 8×4rectangular block are determined by selecting the values of quantizedcoefficients in the QM for the square block corresponding to the groupas the quantized coefficients which make up the group, and arranging theselected values in the group.

It is to be noted that the method of deriving quantized coefficients ineach group in the QM for the rectangular block is not limited to theexample, and another method may be used. For example, quantizedcoefficients may be derived by performing linear interpolation, or thelike, with reference to values of quantized coefficients in aneighboring frequency domain so that the quantized coefficients in thegroup are sequential values. When a decimal value is obtained as aresult of calculation of any of these values, it is to be noted that thedecimal value may be rounded into an integer value using rounding-up,rounding-down, rounding-off, or the like.

It is to be noted that methods of deriving quantized coefficients ineach of the groups in a QM for a rectangular block may be switchedaccording to a frequency domain in which the group is located in the QMfor the rectangular block. For example, quantized coefficients in eachof the groups located at the low-frequency side may be derived so thatthe values of the quantized coefficients are comparatively small values,and quantized coefficients in each of the groups located at thehigh-frequency side may be derived so that the values of the quantizedcoefficients are comparatively large values.

It is to be noted that the lowest-frequency component (upper-leftquantized coefficients in the example in FIG. 54 ) in a QM for arectangular block to be generated may be described in a stream and bedirectly set from the stream, instead of deriving a QM for a squareblock. In that case, the amount of information to be described in thestream increases, and thus the amount of codes of the header areainevitably increases. However, it is possible to directly control thequantized coefficient of the lowest-frequency component which affects aresulting image quality most significantly in the QM, which increasesthe possibility of being able to increase the image quality.

Although the example in the case of generating the QM for therectangular block by vertically up-converting the QM for the squareblock has been described here, it is to be noted that a QM for arectangular block may also be generated by horizontally up-converting aQM for a square block using a method similar to the method in theexample in FIG. 54 .

Another Variation of Aspect 2 Relating to Encoding and Decoding

It is also excellent that a method of switching to one of the firstexample and the second example may be performed according to the size ofa rectangular block to be generated, and the one is used, as the methodof generating a QM for the rectangular block based on a QM for a squareblock. The first example is the method of generating the QM for therectangular block described with reference to FIG. 51 and FIG. 52 , andthe second example method is the method of generating the QM for therectangular block described with reference to FIG. 53 and FIG. 54 . Forexample, there is a method of comparing a size ratio of thevertical-side length and the horizontal-side length of a rectangularblock with a threshold value, and using the first example when thecomparison result is larger than the threshold value and using thesecond example when the comparison result is smaller than the thresholdvalue (the size ratio is a magnification in down-conversion orup-conversion). Alternatively, there is a method of describing, in astream, a flag indicating which one of the schemes of the first exampleand the second example is used for each size of a rectangular block, andperforms switching according to the flag. In this way, since it ispossible to switch between down-conversion processing and up-conversionprocessing according to the size of a rectangular block, it is possibleto generate a more appropriate QM for the rectangular block.

It is also excellent that up-conversion processing and down-conversionprocessing may be used in combination for one rectangular block, insteadof switching between up-conversion processing and down-conversionprocessing for each of the sizes of rectangular blocks. For example, itis also excellent that a QM for a 32×64 rectangular block is generatedby horizontally up-converting a QM for a 32×32 square block, and then aQM for a 16×64 rectangular block is generated by horizontallydown-converting the QM for the 32×64 rectangular block.

Alternatively, two-dimensional up-conversion processing may be performedon one rectangular block. For example, it is also excellent that a QMfor a 32×16 rectangular block is generated by vertically up-converting aQM for a 16×16 square block, and then a QM for a 32×64 rectangular blockis generated by horizontally up-converting the QM for the 32×16rectangular block.

It is to be noted that, two-dimensional down-conversion processing maybe performed on one rectangular block. For example, it is also excellentthat a QM for a 64×32 rectangular block is generated by horizontallydown-converting a QM for a 64×64 square block, and then a QM for a 16×32rectangular block is generated by vertically down-converting the QM forthe 64×32 rectangular block.

Effects of Aspect 2 Relating to Encoding and Decoding

With the configuration explained with reference to FIG. 49 and FIG. 50 ,also in the encoding scheme for pictures including rectangular blockswhich have various shapes, encoder 100 and decoder 200 according toAspect 2 of the present disclosure are capable of encoding and decodingthe rectangular blocks by describing, in a stream, only QMscorresponding to square blocks without describing, in the stream, QMscorresponding to the rectangular blocks having various shapes. In otherwords, encoder 100 and decoder 200 according to Aspect 2 of the presentdisclosure do not require that the QMs for the rectangular blocks aredescribed in the stream, which enables reduction in amount of codes ofthe header area. Furthermore, encoder 100 and decoder 200 according toAspect 2 of the present disclosure are capable of generating the QMscorresponding to the rectangular blocks based on the QMs correspondingto the square blocks, which makes it possible to use appropriate QMsalso for the rectangular blocks without increasing the amount of codesof the header area. In addition, decoder 200 according to Aspect 2 ofthe present disclosure generates quantization matrices corresponding torectangular blocks based on corresponding square blocks, and thus doesnot always need to decode any quantization matrices corresponding torectangular blocks. Thus, encoder 100 according to Aspect 2 of thepresent disclosure is capable of efficiently quantizing the rectangularblocks having various shapes, which makes it possible to increase thecoding efficiency. Furthermore, decoder 200 according to Aspect 2 of thepresent disclosure is capable of efficiently inverse-quantizing therectangular blocks, which makes it possible to increase the processingefficiency.

This aspect may be performed in combination with at least part of otheraspects. Part of processing indicated in the flow chart relating to thisaspect, a part of the configuration of each apparatus, a part of syntax,etc. may be combined with counterparts in other aspects, and a combinedaspect may be performed.

ASPECT 3

Hereinafter, descriptions are given of encoder 100, decoder 200, anencoding method, and a decoding method according to Aspect 3 of thepresent disclosure.

Effects of Aspect 3 Relating to Encoding and Decoding

FIG. 55 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in encoder 100 according to Aspect 3.It is to be noted that encoder 100 described here performs encoding foreach square or rectangular block obtained by splitting a frame.

First, in Step S301, quantizer 108 generates, for each of square blocksor rectangular blocks which have various block sizes, a QM correspondingto the size of a domain including effective transform coefficients(hereinafter also referred to as an effective transform coefficientdomain) in the block. In other words, quantizer 108 performsquantization using a quantization matrix only for a plurality oftransform coefficients in a predetermined domain at a low-frequencydomain side among the plurality of transform coefficients included in acurrent block to be processed.

Entropy encoder 110 describes, in a stream, a signal relating to a QMcorresponding to the effective transform coefficient domain generated inStep S301. In other words, entropy encoder 110 encodes, in thebitstream, the signal relating to the quantization matrix correspondingonly to the transform coefficients in the predetermined range at thelow-frequency domain side. It is to be noted that quantizer 108 maygenerate the QM corresponding to the effective transform coefficientdomain based on values which have been defined by a user and pre-set inencoder 100, or may adaptively generate the QM corresponding to theeffective transform coefficient domain using encoded information of analready encoded picture. In addition, the QM corresponding to theeffective transform coefficient domain may be encoded in an area in thestream. The area is one of a sequence header area, a picture headerarea, a slice header area, a supplemental information area, or anotherarea storing another parameter. The QM corresponding to the effectivetransform coefficient domain does not always need to be described in thestream. At this time, quantizer 108 may use default values which havebeen pre-defined in a standard as the values of the QM corresponding tothe effective transform coefficient domain.

It is to be noted that, as explained with reference to FIG. 55 , theprocessing in Step S301 may be performed on the blocks collectively atthe time of starting processing of a sequence, a picture, or a slice, orperformed each time when part of the processing is performed inprocessing of a unit that is a block. In addition, the QM generated inStep S301 may comprise a plurality of kinds of QMs for blocks having thesame size which are generated under conditions such as whether each QMis for a luminance block or for a chrominance block, each QM is for anintra-prediction block or for an inter-prediction block, and under otherconditions.

It is to be noted that, in the processing flow indicated in FIG. 55 ,the processing other than the processing in Step S301 is in theblock-based loop processing, and thus is similar to the processing inAspect 2 explained with reference to FIG. 49 .

In this way, it is possible to encode the current block to be processedhaving a block size, for which only the partial domain at thelow-frequency side among the transform coefficients included in thecurrent block is defined as a domain including effective transformcoefficients, without wastefully describing, in the stream, a signalrelating to a QM corresponding to a domain including the remainingineffective transform coefficients. Accordingly, it is possible toreduce the amount of codes of the header area, which increases thepossibility of being able to increase the coding efficiency.

It is to be noted that this processing flow is one example, and thus itis to be noted that the processing order described may be changed, partof the processing may be removed, and processing which is not describedmay be added.

FIG. 56 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in decoder 200 according to Aspect 3.It is to be noted that decoder 200 described here performs decoding foreach square or rectangular block obtained by splitting a frame.

First, in Step S401, entropy decoder 202 decodes a signal relating to aQM corresponding to an effective transform coefficient domain from astream, and generates the QM corresponding to the effective transformcoefficient domain using the signal relating to the QM corresponding tothe decoded effective transform coefficient domain. The QM correspondingto the effective transform coefficient domain in each of current blockshaving various block sizes is a QM corresponding to the size of theeffective transform coefficient domain in the current block. It is to benoted that, the QM corresponding to the effective transform coefficientdomain may be decoded from an area in the stream. The area is one of asequence header area, a picture header area, a slice header area, asupplemental information area, or another area storing anotherparameter. At this time, for example, default values which have beenpre-defined in a standard may be used as values of the QM correspondingto the effective transform coefficient domain.

It is to be noted that the processing in Step S401 may be performed onthe blocks collectively at the time of starting processing of asequence, a picture, or a slice, as explained with reference to FIG. 56, or performed each time when part of the processing is performed inprocessing of a unit that is a block. In addition, the QM generated byentropy decoder 202 in Step S401 may comprise a plurality of kinds ofQMs for blocks having the same block size which are generated underconditions such as whether each QM is for a luminance block or for achrominance block, each QM is for an intra-prediction block or for aninter-prediction block, and under other conditions.

It is to be noted that, in the processing flow indicated in FIG. 56 ,the processing other than the processing in Step S401 is in theblock-based loop processing, and thus is similar to the processing inAspect 2 explained with reference to FIG. 50 .

In this way, it is possible to decode the current block to be processedhaving a block size, for which only the partial domain at thelow-frequency side among the transform coefficients included in thecurrent block is defined as a domain including effective transformcoefficients, without wastefully describing, in the stream, a signalrelating to a QM corresponding to a domain including remainingineffective transform coefficients. Accordingly, it is possible toreduce the amount of codes of the header area, which increases thepossibility of being able to increase the coding efficiency.

It is to be noted that this processing flow is one example, and thus itis to be noted that the processing order described may be changed, partof the processing may be removed, and processing which is not describedmay be added.

FIG. 57 is a diagram for explaining an example of a QM corresponding tothe size of an effective transform coefficient domain in each of blockswhich have various block sizes in Step S301 in FIG. 55 and in Step S401in FIG. 56 . It is to be noted that the processing described here iscommon between encoder 100 and decoder 200.

In FIG. 57 , (a) illustrates an example in the case where a currentblock is a square block having a block size of 64×64. Only the 32×32domain at a low-frequency side indicated by the diagonal lines in thediagram is the effective transform coefficient domain. In the currentblock, transform coefficients in the domain other than the effectivetransform coefficient domain are forcedly set to 0. In other words,since the transform coefficients are made ineffective, quantizationprocessing and inverse quantization processing are unnecessary. In otherwords, encoder 100 and decoder 200 according to Aspect 3 of the presentdisclosure generates only the 32×32 QM corresponding to the 32×32 domainat the low-frequency side indicated by the diagonal lines in thediagram.

Next, in FIG. 57 , (b) illustrates an example in the case where acurrent block is a rectangular block having a block size of 64×32. As inthe example of (a) in FIG. 57 , in the example of (b) in FIG. 57 ,encoder 100 and decoder 200 generate only a 32×32 QM corresponding tothe 32×32 domain at the low-frequency side.

Next, in FIG. 57 , (c) illustrates an example in the case where acurrent block is a rectangular block having a block size of 64×16.Unlike the example of (a) in FIG. 57 , in the example of (c) in FIG. 57, the vertical block size is only 16, and thus encoder 100 and decoder200 generate only a 32×16 QM corresponding to the 32×16 domain at thelow-frequency side.

In this way, when one of the vertical sides or the horizontal sides of acurrent block are longer than 32, the transform coefficients in thedomain outside the domain whose sides are all within 32 are invalidated,and the domain whose sides are all within 32 which is the effectivetransform coefficient domain are handled as a processing target ofquantization and inverse quantization, and the processing target issubjected to generation of quantized coefficients in the QM, andencoding in and decoding from a stream of a signal relating to the QM.

In this way, encoding and decoding are possible without wastefullydescribing, in the stream, the signal relating to the QM correspondingto the ineffective transform coefficient domain, which makes it possibleto reduce the amount of codes of the header area. This increases thepossibility of being able to increase the coding efficiency.

It is to be noted that the sizes of the effective transform coefficientdomains explained with reference to FIG. 57 are examples, and thuseffective transform coefficient domains having sizes other than theexample sizes may be used. For example, a domain having at most 32×32size may be handled as an effective transform coefficient domain when acurrent block is a luminance block, and a domain having at most 16×16size may be handled as an effective transform coefficient domain when acurrent block is a chrominance block. Alternatively, a domain having atmost 32×32 size may be handled as an effective transform coefficientdomain when a current block has long sides each having a length of 64,and a domain having at most 62×62 size may be handled as an effectivetransform coefficient domain when a current block has long sides eachhaving a length of 128 or 256.

It is to be noted that the QM corresponding to only the effectivetransform coefficient domain explained with reference to FIG. 57 may begenerated after coefficients of a quantization matrix corresponding toall frequency components in a square block or a rectangular block areonce generated by performing similar processing according to the methodexplained in Aspect 3. In this case, the amount of a signal relating tothe QM to be described in a stream does not change from the amount of asignal in the case where the method explained in Aspect 3 is performed.Furthermore, it is possible to skip quantization processing on thedomain other than the effective transform coefficient domain whilemaintaining the advantage of being able to generate all the QMs for thesquare or rectangular blocks directly using the method explained inAspect 3. This increases the possibility of being able to reduce theamount of processing relating to quantization processing.

Effects of the Variation of Aspect 3 Relating to Encoding and Decoding

FIG. 58 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in encoder 100 according to a variationof Aspect 3. It is to be noted that encoder 100 described here performsencoding for each square or rectangular block obtained by splitting aframe.

This variation is obtained by combining the configuration in Aspect 3explained with reference to FIG. 55 and the configuration in Aspect 2explained with reference to FIG. 49 . In this variation, processing inStep S501 and processing in Step S502 are performed instead ofprocessing in Step S301.

First, in Step S501, quantizer 108 generates a QM for a square block. Atthis time, the QM for the square block is a QM corresponding to the sizeof the effective transform coefficient domain in the square block.Entropy encoder 110 described, in the stream, the QM signal for a squareblock generated in Step S501. At this time, the signal relating to theQM described in the stream is a signal relating only to quantizedcoefficients corresponding to the effective transform coefficientdomain.

Next, in Step S502, quantizer 108 generates a QM for a rectangular blockusing the QM for the square block generated in Step S501. It is to benoted that entropy encoder 110 does not describe a signal relating to aQM for a rectangular block in the stream.

It is to be noted that, in the processing flow indicated in FIG. 58 ,the processing other than the processing in Step S501 and the processingin Step S502 is in the block-based loop processing, and thus is similarto the processing in Aspect 2 explained with reference to FIG. 49 .

In this way, also in the encoding scheme for pictures includingrectangular blocks which have various shapes, describing only QMscorresponding to square blocks in the stream enables encoding withoutdescribing QMs corresponding to the rectangular blocks having variousshapes. Furthermore, it is possible to encode the current block to beprocessed having a block size, for which only the domain including someof the transform coefficients included in the current block is definedas a domain including effective transform coefficients (that is, aneffective transform coefficient domain), without wastefully describing,in the stream, a signal relating to a QM of a domain including theremaining ineffective transform coefficients. Accordingly, it ispossible to use the QM for the rectangular block while reducing theamount of codes of the header area, which increases the possibility ofbeing able to increase the coding efficiency.

It is to be noted that this processing flow is one example, and thus itis to be noted that the processing order described may be changed, partof the processing may be removed, and processing which is not describedmay be added.

FIG. 59 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in decoder 200 according to thevariation of Aspect 3. It is to be noted that decoder 200 described hereperforms decoding for each square or rectangular block obtained bysplitting a frame.

This variation is obtained by combining the configuration in Aspect 3explained with reference to FIG. 56 and the configuration in Aspect 2explained with reference to FIG. 50 . In this variation, processing inStep S601 and processing in Step S602 are performed instead ofprocessing in Step S401.

First, in Step S601, entropy decoder 202 decodes the signal relating tothe QM for the square block from the stream to generate the QM for thesquare block using the decoded signal relating to the QM for the squareblock. At this time, the signal relating to the QM for the square blockdecoded from the stream is a signal relating only to quantizedcoefficients corresponding to the effective transform coefficient domainin the QM for the square block. Thus, the QM for the square blockgenerated by entropy decoder 202 is a QM corresponding to the size ofthe effective transform coefficient domain.

Next, in Step S602, entropy decoder 202 generates a QM for a rectangularblock using the QM for the square block generated in Step S601. At thistime, entropy decoder 202 does not decode a signal relating to the QMfor the rectangular block from the stream.

It is to be noted that, in the processing flow indicated in FIG. 59 ,the processing other than the processing in Step S601 and the processingin Step S602 is in the block-based loop processing, and thus is similarto the processing in Aspect 2 explained with reference to FIG. 50 .

In this way, in the encoding scheme for pictures including rectangularblocks which have various shapes, decoding is possible when only signalsrelating to QMs corresponding to square blocks have been described inthe encoding scheme even if signals relating to QMs corresponding to therectangular blocks having various shapes have not been described.Furthermore, it is possible to decode the current block to be processedhaving a block size, for which only the domain including some of thetransform coefficients included in the current block is defined as adomain including effective transform coefficients (that is, an effectivetransform coefficient domain), without wastefully describing, in thestream, a signal relating to a QM of a domain including the remainingineffective transform coefficients. Accordingly, it is possible to usethe QM for the rectangular block while reducing the amount of codes ofthe header area, which increases the possibility of being able toincrease the coding efficiency.

It is to be noted that this processing flow is one example, and thus itis to be noted that the processing order described may be changed, partof the processing may be removed, and processing which is not describedmay be added.

A First Example of a Method of Generating a QM for a Rectangular Blockin the Variation of Aspect 3

FIG. 60 is a diagram for explaining a first example of generating a QMfor a rectangular block based on a QM for a square block in Step S502 inFIG. 58 and in Step S602 in FIG. 59 . It is to be noted that theprocessing described here is common between encoder 100 and decoder 200.

FIG. 60 illustrates, for each of square blocks each having a size in arange from 2×2 to 256×256, the size of a QM for a square block and thesize of a QM for a rectangular block generated based on the QM for thesquare block in association with each other. The example in FIG. 60illustrates, the sizes of current blocks to be processed and the sizesof effective transform coefficient domains in the respective currentblocks. The numerical values described in the parenthesis indicate thesizes of the effective transform coefficient domains in the respectivecurrent blocks. In the case of a rectangular block in which the size ofa current block to be processed and the size of an effective transformcoefficient size are the same, the same processing as in Aspect 2explained with reference to FIG. 49 is performed, and thus it is to benoted that numerical values in the case are omitted in the associationtable indicated in FIG. 60 .

Here, it is characterized in that the length of a long side of each ofrectangular blocks is the same as the length of one side of acorresponding rectangular block, and the rectangular block is smallerthan the square block. In other words, the QM for the rectangular blockis generated by down-converting the QM for the square block.

It is to be noted that FIG. 60 indicates the correlation relationshipbetween the QMs for the square blocks which have various block sizes andthe QMs for the rectangular blocks which are generated based on the QMsfor the square blocks without discriminating luminance blocks andchrominance blocks. The correlation relationship between a QM for asquare block and a QM for a rectangular block adapted to a format to beactually used may be derived appropriately. For example, in the case ofa 4:2:0 format, a luminance block has a size that is twice the size of achrominance block. Thus, when referring to the luminance block in theprocessing of generating the QM for the rectangular block based on theQM for the square block, an available QM for the square blockcorresponds to a square block having a size in a range from 4×4 to256×256. At this time, only a QM corresponding to a rectangular blockhaving a size defined by a short-side length of 4 or more and along-side length of 256 or less is used as the QM for the rectangularblock that is generated based on the QM for the square block. Inaddition, when referring to a chrominance block in the processing ofgenerating the QM for the rectangular block based on the QM for thesquare block, only a QM corresponding to a rectangular block having asize defined by a short-side length of 2 or more and a long-side lengthof 128 or less is used as the QM for the rectangular block that isgenerated based on the QM for the square block. It is to be noted thatthe same details explained with reference to FIG. 51 apply to the caseof a 4:4:4 format, and thus the same explanation is not repeated here.

In this way, the correlation relationship between the QM for the squareblock and the QM for the rectangular block may be appropriately derivedaccording to the format to be actually used.

The sizes of the effective transform coefficient domains described inFIG. 60 are examples, and thus the sizes of effective transformcoefficient domains other than the sizes indicated as examples in FIG.60 may be used.

It is to be noted that the block sizes indicated in FIG. 60 areexamples, and thus block sizes are not limited to the sizes therein. Forexample, block sizes other than the block sizes indicated as examples inFIG. 60 may be used, and only some of the block sizes indicated asexamples in FIG. 60 may be used.

FIG. 61 is a diagram for illustrating a method of generating the QM forthe rectangular block explained with reference to FIG. 60 bydown-converting the corresponding QM for the square block.

In the example in FIG. 61 , a QM corresponding to a 32×32 effectivetransform coefficient domain in a 64×32 rectangular block is generatedbased on a QM corresponding to a 32×32 effective transform coefficientdomain in a 64×64 square block.

First, as illustrated in (a) in FIG. 61 , a QM for an intermediate 64×64square block having a 32×64 effective transform coefficient domain isgenerated by vertically extending a domain with a slop of quantizedcoefficients in the QM corresponding to the 32×32 effective transformcoefficient domain. Examples of extending such a domain with a slopeincludes: a method of extending a domain with a slope of quantizedcoefficients so that the difference value between each of the quantizedcoefficients on the 31st line and a corresponding one of the quantizedcoefficients on the 32nd line is the difference value between followingneighboring quantized coefficients; and a method of extending a domainwith a slope of quantized coefficients by deriving a variation amountbetween (i) the difference value between each of the quantizedcoefficients on the 30th line and a corresponding one of the quantizedcoefficients on the 32st line and (ii) the difference value between eachof the quantized coefficients on the 31st line and a corresponding oneof the quantized coefficients on the 32nd line is the difference valuebetween following neighboring quantized coefficients, and correcting, bythe variation amount, the difference value between following neighboringquantized coefficients. As illustrated in (b) in FIG. 61 , a QM for a64×32 rectangular block is generated by down-converting the QM for theintermediate 64×64 square block having the 32×64 effective transformcoefficient domain, using a method similar to the method explained withreference to FIG. 52 . At this time, the resulting effective transformcoefficient domain is a 32×32 domain with diagonal lines in the QM forthe 64×32 rectangular block illustrated in (c) in FIG. 61 .

Although the example in the case of generating the QM for therectangular block by vertically down-converting the QM for the squareblock has been described here, it is to be noted that a QM for arectangular block may also be generated by horizontally down-convertinga QM for a square block using a method similar to the method in theexample in FIG. 61 .

Here, explanation has been given of generating the QM for therectangular block in two-stage steps via the QM for the intermediatesquare block. However, it is to be noted that a QM for a rectangularblock may be directly generated based on a QM for a square block havingan effective transform coefficient domain by using a conversionexpression, or the like that derives a processing result similar to theresult in the example in FIG. 61 , without the intermediate QM for thesquare block.

A Second Example of a Method of Generating a QM for a Rectangular Blockin the Variation of Aspect 3

FIG. 62 is a diagram for explaining a second example of generating a QMfor a rectangular block based on a QM for a square block in Step S502 inFIG. 58 and in Step S602 in FIG. 59 . It is to be noted that theprocessing described here is common between encoder 100 and decoder 200.

FIG. 62 illustrates, for each of square blocks each having a size in arange from 2×2 to 256×256, the size of a QM for a square block and thesize of a QM for a rectangular block generated based on the QM for thesquare block in association with each other. The example in FIG. 62illustrates, the sizes of current blocks to be processed and the sizesof effective transform coefficient domains in the respective currentblocks. The numerical values described in the parenthesis indicate thesizes of the effective transform coefficient domains in the respectivecurrent blocks. In the case of a rectangular block in which the size ofa current block and the size of the effective transform coefficient sizeare the same, the same processing as in Aspect 2 explained withreference to FIG. 53 is performed, and thus it is to be noted thatnumerical values in the case are omitted in the association tableindicated in FIG. 62 .

Here, it is characterized in that the length of a short side of each ofrectangular blocks is the same as the length of one side of acorresponding square block, and the rectangular block is larger than thesquare block. In other words, the QM for the rectangular block isgenerated by up-converting the QM for the square block.

It is to be noted that FIG. 62 indicates the correlation relationshipbetween the QMs for the square blocks which have various block sizes andthe QMs for the rectangular blocks which are generated based on the QMsfor the square blocks without discriminating luminance blocks andchrominance blocks. The correlation relationship between a QM for asquare block and a QM for a rectangular block adapted to a format to beactually used may be derived appropriately. For example, in the case ofa 4:2:0 format, a chrominance block has a size that is twice the size ofa luminance block. Thus, in the case of 4:2:0 format, when referring toa luminance block in the processing of generating the QM for therectangular block based on the QM for the square block, only a QMcorresponding to a rectangular block having a size defined by ashort-side length of 4 or more and a long-side length of 256 or less isused as the QM for the rectangular block that is generated based on theQM for the square block. In addition, when referring to a chrominanceblock in the processing of generating the QM for the rectangular blockbased on the QM for the square block, only a QM corresponding to arectangular block having a size defined by a short-side length of 2 ormore and a long-side length of 128 or less is used as the QM for therectangular block that is generated based on the QM for the squareblock. It is to be noted that the same details explained with referenceto FIG. 61 apply to the case of a 4:4:4 format, and thus the sameexplanation is not repeated here.

In this way, the correlation relationship between the QM for the squareblock and the QM for the rectangular block may be appropriately derivedaccording to the format to be actually used.

The sizes of the effective transform coefficient domains described inFIG. 62 are examples, and thus the sizes of effective transformcoefficient domains other than the sizes indicated as examples in FIG.62 may be used.

It is to be noted that the block sizes indicated in FIG. 62 areexamples, and thus block sizes are not limited to the sizes therein. Forexample, block sizes other than the block sizes indicated as examples inFIG. 62 may be used, and only some of the block sizes indicated in FIG.62 may be used.

FIG. 63 is a diagram for illustrating a method of generating the QM forthe rectangular block explained with reference to FIG. 62 byup-converting the corresponding QM for a square block.

In the example in FIG. 63 , a QM corresponding to a 32×32 effectivetransform coefficient domain in a 64×32 rectangular block is generatedbased on a QM corresponding to a 32×32 effective transform coefficientdomain in a 32×32 square block.

First, as illustrated in (a) in FIG. 63 , a QM for an intermediate 64×32rectangular block is generated by up-converting the QM for the 32×32square block using a method similar to the method explained withreference to FIG. 54 . At this time, the effective transform coefficientdomain is also up-converted to a 64×32 effective transform coefficientdomain.

Next, as illustrated in (b) in FIG. 63 , a QM for a 64×32 rectangularblock having a 32×32 effective transform coefficient block is generatedby extracting only the 32×32 domain at the low-frequency side from the64×32 effective transform coefficient domain.

Although the example in the case of generating the QM for therectangular block by horizontally up-converting the QM for the squareblock has been described here, it is to be noted that a QM for arectangular block may also be generated by vertically up-converting a QMfor a square block using a method similar to the method in the examplein FIG. 60 .

Here, explanation is given of generating the QM for the rectangularblock in two-stage steps via the QM for the intermediate rectangularblock. However, it is to be noted that a QM for a rectangular block maybe directly generated based on a QM for a square block by using aconversion expression, or the like that derives a processing resultsimilar to the result in the example in FIG. 62 , without the QM for anintermediate rectangular block.

A Variation of Aspect 3 Relating to Encoding and Decoding

It is also excellent that switching to one of the first example methodand the second example method may be performed according to the size ofa rectangular block to be generated, and the one is used, as the methodof generating a QM for a rectangular block based on a QM for a squareblock. The first example method is the method of generating the QM forthe rectangular block described with reference to FIG. 60 and FIG. 61 ,and the second example method is the method of generating the QM for therectangular block described with reference to FIG. 62 and FIG. 63 . Forexample, there is a method of comparing a size ratio of thevertical-side length and the horizontal-side length of a rectangularblock with a threshold value, and using the first example when thecomparison result is larger than the threshold value and using thesecond example when the comparison result is smaller than the thresholdvalue (the size ratio is a magnification in down-conversion orup-conversion). Alternatively, there is a method of describing, in astream, a flag indicating which one of the schemes of the first exampleand the second example is used for each size of a rectangular block, andperforms switching according to the flag. In this way, since it ispossible to switch between down-conversion processing and up-conversionprocessing according to the size of the rectangular block, it ispossible to generate a more appropriate QM for the rectangular block.

Effects of Aspect 3 Relating to Encoding and Decoding and the Variationof Aspect 3

With the configuration explained with reference to FIG. 55 and FIG. 56 ,encoder 100 and decoder 200 according to Aspect 3 of the presentdisclosure are capable of encoding and decoding a current rectangularblock to be processed having a block size, for which only the domainincluding some of the transform coefficients included in the currentblock is defined as an effective transform coefficient domain, withoutdescribing, in the stream, a signal relating to a QM of a domainincluding the remaining ineffective transform coefficients. Accordingly,it is possible to reduce the amount of codes of the header area, whichincreases the possibility of being able to increase the codingefficiency.

Furthermore, with the configuration explained with reference to FIG. 58and FIG. 59 , also in the encoding scheme for pictures including therectangular blocks which have various shapes, encoder 100 and decoder200 according to Aspect 3 of the present disclosure are capable ofencoding and decoding rectangular blocks by describing, in a stream,only QMs corresponding to square blocks without describing, in thestream, QMs corresponding to the rectangular blocks having the variousshapes. In other words, encoder 100 and decoder 200 according to thevariation of Aspect 3 of the present disclosure are capable ofgenerating the QMs corresponding to the rectangular blocks based on theQMs corresponding to the square blocks, which makes it possible to useappropriate QMs also for the rectangular blocks without increasing theamount of codes of the header area. Thus, encoder 100 and decoder 200according to Aspect 3 of the present disclosure are capable ofefficiently quantizing the rectangular blocks having the various shapes,which increases the possibility of being able to increase the codingefficiency.

This aspect may be performed in combination with at least part of otheraspects. Part of processing indicated in the flow chart relating to thisaspect, a part of the configuration of each apparatus, a part of syntax,etc. may be combined with counterparts in other aspects, and a combinedaspect may be performed.

ASPECT 4

Hereinafter, descriptions are given of encoder 100, decoder 200, anencoding method, and a decoding method according to Aspect 4 of thepresent disclosure.

Encoding and Decoding According to Aspect 4

FIG. 64 is a flow chart indicating one example of a flow of encodingusing a quantization matrix (QM) in encoder 100 according to Aspect 4.It is to be noted that encoder 100 described here performs encoding foreach square or rectangular block obtained by splitting a frame.

First, in Step S701, quantizer 108 generates a QM corresponding todiagonal components in a current block to be processed (hereinafter, theQM is also referred to as a QM having only diagonal components), andgenerates a QM corresponding to a current block to be processed, basedon values of quantized coefficients of the QM having only the diagonalcomponents in each of the square block and rectangular blocks havingvarious shapes, by using a common method to be described below. In otherwords, quantizer 108 generates the quantization matrix for the currentblock, based on the diagonal components in the QM. The quantizationmatrix for the current block is for transform coefficients arrangedsequentially in the diagonal direction in the current block among theplurality of transform coefficients in the current block. It is to benoted that using the common method means using the common method for allcurrent blocks to be processed regardless of the shapes and sizes of theblocks. In addition, the diagonal components means a plurality ofcoefficients on the diagonal line that extends from the low-frequencyside to the high-frequency side in each current block.

Entropy encoder 110 describes, in a stream, a signal relating to a QMhaving only diagonal components generated in Step S701. In other words,entropy encoder 110 encodes a signal relating to the diagonal componentsof the quantization matrix into a bitstream.

It is to be noted that quantizer 108 may generate values of quantizedcoefficients in the QM having only the diagonal components, based onvalues which have been defined by a user and pre-set to encoder 100, ormay adaptively generate the QM having only the diagonal components usingencoded information of a picture which has been already encoded. Inaddition, the QM having only the diagonal components may be encoded inan area in the stream. The area is one of a sequence header area, apicture header area, a slice header area, a supplemental informationarea, or another area storing another parameter. It is to be noted thatthe QM having only the diagonal components does not always need to bedescribed in a stream. At this time, quantizer 108 may use defaultvalues which have been pre-defined in a standard as values of the QMhaving only the diagonal components.

It is to be noted, as explained with reference to FIG. 64 , that theprocessing in Step S701 may be performed on the blocks collectively atthe time of starting processing of a sequence, a picture, or a slice, orperformed each time when part of the processing is performed inprocessing of a unit that is a block. In addition, the QM generated inStep S701 may comprise a plurality of kinds of QMs for blocks having thesame block size which are generated under conditions such as whethereach QM is for a luminance block or for a chrominance block, each QM isfor an intra-prediction block or for an inter-prediction block, andunder other conditions.

It is to be noted that, in the processing flow indicated in FIG. 64 ,the processing other than the processing in Step S701 is in theblock-based loop processing, and thus is similar to the processing inAspect 2 explained with reference to FIG. 49 .

In this way, it is possible to encode each of the current blocks whichhave various block sizes by describing, in the stream, only thequantized coefficients of the diagonal components in the QM withoutdescribing, in the stream, all the quantized coefficients in the QM ofthe current block. Accordingly, it is possible to generate and use theQM corresponding to each current block without significantly increasingthe amount of codes of the header area also in the encoding scheme usingblocks having many shapes which include rectangular blocks. Thisincreases the possibility of being able to increase the codingefficiency.

It is to be noted that this processing flow is one example, and thus itis to be noted that the processing order described may be changed, partof the processing may be removed, and processing which is not describedmay be added.

FIG. 65 is a flow chart indicating one example of a flow of decodingusing a quantization matrix (QM) in decoder 200 according to Aspect 4.It is to be noted that decoder 200 described here performs decoding foreach square or rectangular block obtained by splitting a frame.

First, in Step S801, entropy decoder 202 decodes a signal relating to aQM having only diagonal components from a stream, and generates a QM forone of current blocks having various shapes such as square blocks andrectangular blocks suitably for the size of each block using a signalrelating to the QM having only the diagonal components which have beendecoded, according to a common method to be described below. It is to benoted that the QM having only the diagonal components may be decodedfrom an area in the stream. The area is one of a sequence header area, apicture header area, a slice header area, a supplemental informationarea, or another area storing another parameter. It is to be noted thatthe QM having only the diagonal components does not always need to bedescribed in a stream. At this time, for example, default values whichhave been pre-defined in a standard may be used as values of only thediagonal components in the QM.

It is to be noted, as explained with reference to FIG. 65 , that theprocessing in Step S801 may be performed on the blocks collectively atthe time of starting processing of a sequence, a picture, or a slice, orperformed each time when part of the processing is performed inprocessing of a unit that is a block. In addition, the QM generated byentropy decoder 202 in Step S801 may comprise a plurality of kinds ofQMs for each of blocks having the same block size which are generatedunder conditions such as whether each QM is for a luminance block or fora chrominance block, each QM is for an intra-prediction block or for aninter-prediction block, and under other conditions.

It is to be noted that, in the processing flow indicated in FIG. 65 ,the processing other than the processing in Step S801 is in theblock-based loop processing, and thus is similar to the processing inAspect 2 explained with reference to FIG. 50 .

In this way, it is possible to perform decoding when only the quantizedcoefficients of the diagonal components in the QM for the current blockincluded in the current blocks which have various block sizes have beendescribed in the stream even if not all the quantized coefficients inthe QM have been described in the stream. Accordingly, it is possible toreduce the amount of codes of the header area, which increases thepossibility of being able to increase the coding efficiency.

It is to be noted that this processing flow is one example, and thus itis to be noted that the processing order described may be changed, partof the processing may be removed, and processing which is not describedmay be added.

FIG. 66 is a diagram for explaining one example of generating, in eachof Step S701 in FIG. 64 and in Step S801 in FIG. 65 , a QM for a currentblock to be processed having one of various block sizes, based on valuesof quantized coefficients of a QM having only diagonal components in thecurrent blocks using a common method to be described below. It is to benoted that the processing described here is common between encoder 100and decoder 200.

Encoder 100 and decoder 200 according to Aspect 4 of the presentdisclosure generate a quantization matrix (QM) for a current block byduplicating each of the plurality of matrix elements of the diagonalcomponents in the current block in the horizontal direction and thevertical direction. More specifically, encoder 100 and decoder 200generate the QM for the current block by directly extending the valuesof quantized coefficients in the QM having the diagonal components bothin the upper direction and the lower direction, in other words,arranging the same values sequentially.

Although the method of generating the QM for the current block in thecase where the current block is a square block has been described here,it is to be noted that a QM for a current block may be generated basedon the values of quantized coefficients of a QM having diagonalcomponents, similarly to the example in FIG. 66 also in the case wherethe current block is a rectangular block.

FIG. 67 is a diagram for explaining another example of generating, ineach of Step S701 in FIG. 64 and in Step S801 in FIG. 65 , QMs for acurrent block to be processed having one of various block sizes, basedon values of quantized coefficients of a QM having only diagonalcomponents in the current block using a common method to be describedbelow. It is to be noted that the processing described here is commonbetween encoder 100 and decoder 200.

Encoder 100 and decoder 200 according to Aspect 4 of the presentdisclosure may generate a quantization matrix for a current block byduplicating each of the plurality of matrix elements of the diagonalcomponents of the current block in a diagonal direction. Morespecifically, encoder 100 and decoder 200 generate the QM for thecurrent block by directly extending the values of quantized coefficientsin the QM having the diagonal components both in the lower leftdirection and the upper right direction, in other words, arranging thesame values sequentially.

At this time, encoder 100 and decoder 200 may generate the QM for thecurrent block by duplicating each of quantized coefficients in thediagonal direction using also quantized coefficients of componentsneighboring the diagonal components in addition to the quantizedcoefficients of the diagonal components. In other words, thequantization matrix (QM) for the current block may be generated based onthe plurality of matrix elements of the diagonal components and thematrix elements located neighboring the diagonal components. In thisway, even in the case where it is difficult to pad all the quantizedcoefficients in the current block using only the diagonal components, itis possible to pad all the quantized coefficients using the quantizedcoefficients of the components neighboring the diagonal components. Itis to be noted that the components neighboring the diagonal componentsare, for example, components each of which neighbors any one of theplurality of coefficients on the diagonal line that extends from thelow-frequency side to the high-frequency side in the current block.

For example, the quantized coefficients of the components neighboringthe diagonal components are quantized coefficients at the locationsillustrated in FIG. 67 . Encoder 100 and decoder 200 may encode, decode,and set, in the stream, a signal relating to the quantized coefficientsof the components neighboring the diagonal components, or may derive andset quantized coefficients by performing, for example, interpolationbased on values of neighboring quantized coefficients among thequantized coefficients of the diagonal components, without encoding anddecoding such a signal in and from the stream.

Although the method of generating the QM for the current block in thecase where the current block is the square block has been describedhere, it is to be noted that a QM for a current block may be generatedbased on the values of quantized coefficients of a QM having diagonalcomponents, similarly to the example in FIG. 67 also in the case where acurrent block is a rectangular block.

Another Variation of Aspect 4 Relating to Encoding and Decoding

Although the method of generating the quantized coefficients of theentire QM of the current block based on the quantized coefficients ofthe QM having the diagonal components has been described in each of theexamples in FIG. 66 and FIG. 67 , it is also excellent that only thequantized coefficients of a part of the QM in the current block may begenerated based on the quantized coefficients of the QM having thediagonal components. For example, it is also excellent that all thequantized coefficients included in a QM corresponding to a low-frequencyside domain in a current block is encoded in and decoded from a stream,and only the quantized coefficients of a QM corresponding to anintermediate-frequency side domain and a high-frequency side domain inthe current block may be generated based on the quantized coefficientsof the QM having the diagonal components in the current block.

It is to be noted that a method of generating a QM for a rectangularblock based on a QM for a square block may be obtained by combining themethod according to Aspect 4 explained with reference to FIG. 64 andFIG. 65 and the method according to Aspect 2 explained with reference toFIG. 49 and FIG. 50 . For example, it is also excellent that the QM forthe square block is generated based on the values of quantizedcoefficients of the QM having only the diagonal components in the squareblock by performing one of the above-described two common methods asexplained in Aspect 4, and the QM for the rectangular block may begenerated using the QM for the square block generated as explained inAspect 2.

It is to be noted that a method of generating a QM for a rectangularblock based on a QM for a square block may be obtained by combining themethod according to Aspect 4 explained with reference to FIG. 64 andFIG. 65 and the method according to Aspect 3 explained with reference toFIG. 55 and FIG. 56 . For example, the QM corresponding to the size ofthe effective transform coefficient domain in each of the blocks whichhave various block sizes may be generated based on the values of thequantized coefficients of the QM having only diagonal components in theeffective transform coefficient domain by performing one of theabove-described common methods.

Effects of Aspect 4 Relating to Encoding and Decoding

With the configuration explained with reference to FIG. 64 and FIG. 65 ,encoder 100 and decoder 200 according to Aspect 4 of the presentdisclosure are capable of encoding and decoding each of the currentblocks which have various block sizes by describing, in a stream, onlythe quantized coefficients of the QM having the diagonal components ofthe current block even if not all the quantized coefficients of the QMof the current block have been described in the stream. Accordingly, itis possible to reduce the amount of codes of the header area, whichincreases the possibility of being able to increase the codingefficiency.

This aspect may be performed by combining at least part of the otheraspects in the present disclosure. In addition, this aspect may beperformed by combining, with other aspects, part of the processesindicated in any of the flow charts according to the aspect, part of theconfiguration of any of the devices, part of syntaxes, etc.

Other Examples

Encoder 100 and decoder 200 in each of the above-described examples maybe used as an image encoder and an image decoder, respectively, or maybe used as a video encoder and a video decoder, respectively.

Alternatively, each of encoder 100 and decoder 200 may be used as aprediction device. In other words, each of encoder 100 and decoder 200may correspond to only inter predictor 126 and inter predictor 218. Theother constituent elements may be included in other devices.

In addition, at least a part of each of the examples described above maybe used as an encoding method or a decoding method, may be used as aprediction method, or may be used as another method.

In addition, each constituent element may be circuitry as describedabove. Circuits may compose circuitry as a whole, or may be separatecircuits. Alternatively, each constituent element may be implemented asa general processor, or may be implemented as an exclusive processor.

In addition, the process that is executed by a particular constituentelement may be executed by another constituent element. In addition, theprocessing execution order may be modified, or a plurality of processesmay be executed in parallel. In addition, an encoder and decoder mayinclude encoder 100 and decoder 200.

In addition, each constituent element may be configured with dedicatedhardware, or may be implemented by executing a software program suitablefor the constituent element. Each constituent element may be implementedby a program executer such as a CPU or a processor reading and executinga software program recorded on a recording medium such as a hard disc ora semiconductor memory.

More specifically, each of encoder 100 and decoder 200 may includeprocessing circuitry and storage which is electrically coupled to theprocessing circuitry and is accessible from the processing circuitry.For example, the processing circuitry corresponds to processor al or b1, and the storage corresponds to memory a2 or b 2.

The processing circuitry includes at least one of the dedicated hardwareand the program executer, and executes processing using the storage. Inaddition, the storage stores a software program which is executed by theprogram executer when the processing circuitry includes the programexecuter.

Here, the software which implements either encoder 100, decoder 200, orthe like described above is a program indicated below.

For example, the program may cause a computer to execute an encodingmethod including: performing quantization on a plurality of transformcoefficients of a current block to be encoded, using a quantizationmatrix when orthogonal transform is performed on the current block andsecondary transform is not performed on the current block; andperforming quantization on the plurality of transform coefficients ofthe current block without using the quantization matrix when orthogonaltransform is not performed on the current block and when both orthogonaltransform and secondary transform are performed on the current block.

For example, the program may cause a computer to execute a decodingmethod including: performing inverse quantization on a plurality oftransform coefficients of a current block to be decoded, using aquantization matrix when inverse orthogonal transform is performed onthe current block and inverse secondary transform is not performed onthe current block; and performing inverse quantization on the pluralityof transform coefficients of the current block without using thequantization matrix when inverse orthogonal transform is not performedon the current block and when both inverse orthogonal transform andinverse secondary transform are performed on the current block.

Although aspects of encoder 100 and decoder 200 have been describedbased on the representative examples, aspects of encoder 100 and decoder200 are not limited to the representative examples. The scope of theaspects of encoder 100 and decoder 200 may encompass embodimentsobtainable by adding, to any of these examples, various kinds ofmodifications that a person skilled in the art would arrive at withoutdeviating from the scope of the present disclosure and embodimentsconfigurable by arbitrarily combining constituent elements in differentexamples.

One or more of the aspects disclosed herein may be performed bycombining at least part of the other aspects in the present disclosure.In addition, one or more of the aspects disclosed herein may beperformed by combining, with other aspects, part of the processesindicated in any of the flow charts according to the aspects, part ofthe configuration of any of the devices, part of syntaxes, etc.

Implementations and Applications

As described in each of the above embodiments, each functional oroperational block may typically be realized as an MPU (micro processingunit) and memory, for example. Moreover, processes performed by each ofthe functional blocks may be realized as a program execution unit, suchas a processor which reads and executes software (a program) recorded ona recording medium such as ROM. The software may be distributed. Thesoftware may be recorded on a variety of recording media such assemiconductor memory. Note that each functional block can also berealized as hardware (dedicated circuit). Various combinations ofhardware and software may be employed.

The processing described in each of the embodiments may be realized viaintegrated processing using a single apparatus (system), and,alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments will be described, aswell as various systems that implement the application examples. Such asystem may be characterized as including an image encoder that employsthe image encoding method, an image decoder that employs the imagedecoding method, or an image encoder-decoder that includes both theimage encoder and the image decoder. Other configurations of such asystem may be modified on a case-by-case basis.

Usage Examples

FIG. 68 illustrates an overall configuration of content providing systemex 100 suitable for implementing a content distribution service. Thearea in which the communication service is provided is divided intocells of desired sizes, and base stations ex 106, ex 107, ex 108, ex109, and ex 110, which are fixed wireless stations in the illustratedexample, are located in respective cells.

In content providing system ex 100, devices including computer ex 111,gaming device ex 112, camera ex 113, home appliance ex 114, andsmartphone ex 115 are connected to internet ex 101 via internet serviceprovider ex 102 or communications network ex 104 and base stations ex106 through ex 110. Content providing system ex 100 may combine andconnect any combination of the above devices. In variousimplementations, the devices may be directly or indirectly connectedtogether via a telephone network or near field communication, ratherthan via base stations ex 106 through ex 110. Further, streaming serverex 103 may be connected to devices including computer ex 111, gamingdevice ex 112, camera ex 113, home appliance ex 114, and smartphone ex115 via, for example, internet ex 101. Streaming server ex 103 may alsobe connected to, for example, a terminal in a hotspot in airplane ex 117via satellite ex116.

Note that instead of base stations ex 106 through ex 110, wirelessaccess points or hotspots may be used. Streaming server ex 103 may beconnected to communications network ex 104 directly instead of viainternet ex 101 or internet service provider ex 102, and may beconnected to airplane ex 117 directly instead of via satellite ex116.

Camera ex 113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex 115 is a smartphone device,cellular phone, or personal handy-phone system (PHS) phone that canoperate under the mobile communications system standards of the 2G, 3G,3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex 114 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex 100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex 103 via, for example, base station ex106. When live streaming, a terminal (e.g., computer ex 111, gamingdevice ex 112, camera ex 113, home appliance ex 114, smartphone ex 115,or a terminal in airplane ex 117) may perform the encoding processingdescribed in the above embodiments on still-image or video contentcaptured by a user via the terminal, may multiplex video data obtainedvia the encoding and audio data obtained by encoding audio correspondingto the video, and may transmit the obtained data to streaming server ex103. In other words, the terminal functions as the image encoderaccording to one aspect of the present disclosure.

Streaming server ex 103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex 111, gamingdevice ex 112, camera ex 113, home appliance ex 114, smartphone ex 115,and terminals inside airplane ex 117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed data maydecode and reproduce the received data. In other words, the devices mayeach function as the image decoder, according to one aspect of thepresent disclosure.

Decentralized Processing

Streaming server ex 103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex 103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client may be dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some type oferror or change in connectivity due, for example, to a spike in traffic,it is possible to stream data stably at high speeds, since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers, orswitching the streaming duties to a different edge server and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex 113 or the like extracts a feature amount(an amount of features or characteristics) from an image, compressesdata related to the feature amount as metadata, and transmits thecompressed metadata to a server. For example, the server determines thesignificance of an object based on the feature amount and changes thequantization accuracy accordingly to perform compression suitable forthe meaning (or content significance) of the image. Feature amount datais particularly effective in improving the precision and efficiency ofmotion vector prediction during the second compression pass performed bythe server. Moreover, encoding that has a relatively low processingload, such as variable length coding (VLC), may be handled by theterminal, and encoding that has a relatively high processing load, suchas context-adaptive binary arithmetic coding (CABAC), may be handled bythe server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos, and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real time.

Since the videos are of approximately the same scene, management and/orinstructions may be carried out by the server so that the videoscaptured by the terminals can be cross-referenced. Moreover, the servermay receive encoded data from the terminals, change the referencerelationship between items of data, or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Furthermore, the server may stream video data after performingtranscoding to convert the encoding format of the video data. Forexample, the server may convert the encoding format from MPEG to VP(e.g., VP9), may convert H.264 to H.265, etc.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

3D, Multi-angle

There has been an increase in usage of images or videos combined fromimages or videos of different scenes concurrently captured, or of thesame scene captured from different angles, by a plurality of terminalssuch as camera ex 113 and/or smartphone ex 115. Videos captured by theterminals may be combined based on, for example, the separately obtainedrelative positional relationship between the terminals, or regions in avideo having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture, either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. The server may separately encodethree-dimensional data generated from, for example, a point cloud and,based on a result of recognizing or tracking a person or object usingthree-dimensional data, may select or reconstruct and generate a videoto be transmitted to a reception terminal, from videos captured by aplurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting a video at a selected viewpointfrom three-dimensional data reconstructed from a plurality of images orvideos. Furthermore, as with video, sound may be recorded fromrelatively different angles, and the server may multiplex audio from aspecific angle or space with the corresponding video, and transmit themultiplexed video and audio.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyes,and perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced, so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server may superimpose virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information. The server may generate superimposed data based onthree-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data typically includes, inaddition to RGB values, an α value indicating transparency, and theserver sets the α value for sections other than the object generatedfrom three-dimensional data to, for example, 0, and may perform theencoding while those sections are transparent. Alternatively, the servermay set the background to a determined RGB value, such as a chroma key,and generate data in which areas other than the object are set as thebackground. The determined RGB value may be predetermined.

Decoding of similarly streamed data may be performed by the client(e.g., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area, or inspect a region in further detail upclose.

In situations in which a plurality of wireless connections are possibleover near, mid, and far distances, indoors or outdoors, it may bepossible to seamlessly receive content using a streaming system standardsuch as MPEG Dynamic Adaptive Streaming over HTTP (MPEG DASH). The usermay switch between data in real time while freely selecting a decoder ordisplay apparatus including the user’s terminal, displays arrangedindoors or outdoors, etc. Moreover, using, for example, information onthe position of the user, decoding can be performed while switchingwhich terminal handles decoding and which terminal handles thedisplaying of content. This makes it possible to map and displayinformation, while the user is on the move in route to a destination, onthe wall of a nearby building in which a device capable of displayingcontent is embedded, or on part of the ground. Moreover, it is alsopossible to switch the bit rate of the received data based on theaccessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal, or when encoded data is copied to an edge server in a contentdelivery service.

Scalable Encoding

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 69 , which is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 69 . Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode based on internalfactors, such as the processing ability on the decoder side, andexternal factors, such as communication bandwidth, the decoder side canfreely switch between low resolution content and high resolution contentwhile decoding. For example, in a case in which the user wants tocontinue watching, for example at home on a device such as a TVconnected to the internet, a video that the user had been previouslywatching on smartphone ex 115 while on the move, the device can simplydecode the same stream up to a different layer, which reduces the serverside load.

Furthermore, in addition to the configuration described above, in whichscalability is achieved as a result of the pictures being encoded perlayer, with the enhancement layer being above the base layer, theenhancement layer may include metadata based on, for example,statistical information on the image. The decoder side may generate highimage quality content by performing super-resolution imaging on apicture in the base layer based on the metadata. Super-resolutionimaging may improve the Signal-to-Noise (SN) ratio while maintainingresolution and/or increasing resolution. Metadata includes informationfor identifying a linear or a non-linear filter coefficient, as used insuper-resolution processing, or information identifying a parametervalue in filter processing, machine learning, or a least squares methodused in super-resolution processing.

Alternatively, a configuration may be provided in which a picture isdivided into, for example, tiles in accordance with, for example, themeaning of an object in the image. On the decoder side, only a partialregion is decoded by selecting a tile to decode. Further, by storing anattribute of the object (person, car, ball, etc.) and a position of theobject in the video (coordinates in identical images) as metadata, thedecoder side can identify the position of a desired object based on themetadata and determine which tile or tiles include that object. Forexample, as illustrated in FIG. 70 , metadata may be stored using a datastorage structure different from pixel data, such as an SEI(supplemental enhancement information) message in HEVC. This metadataindicates, for example, the position, size, or color of the main object.

Metadata may be stored in units of a plurality of pictures, such asstream, sequence, or random access units. The decoder side can obtain,for example, the time at which a specific person appears in the video,and by fitting the time information with picture unit information, canidentify a picture in which the object is present, and can determine theposition of the object in the picture.

Web Page Optimization

FIG. 71 illustrates an example of a display screen of a web page oncomputer ex 111, for example. FIG. 72 illustrates an example of adisplay screen of a web page on smartphone ex 115, for example. Asillustrated in FIG. 71 and FIG. 72 , a web page may include a pluralityof image links that are links to image content, and the appearance ofthe web page may differ depending on the device used to view the webpage. When a plurality of image links are viewable on the screen, untilthe user explicitly selects an image link, or until the image link is inthe approximate center of the screen or the entire image link fits inthe screen, the display apparatus (decoder) may display, as the imagelinks, still images included in the content or I pictures; may displayvideo such as an animated gif using a plurality of still images or Ipictures; or may receive only the base layer, and decode and display thevideo.

When an image link is selected by the user, the display apparatusperforms decoding while, for example, giving the highest priority to thebase layer. Note that if there is information in the Hyper Text MarkupLanguage (HTML) code of the web page indicating that the content isscalable, the display apparatus may decode up to the enhancement layer.Further, in order to guarantee real-time reproduction, before aselection is made or when the bandwidth is severely limited, the displayapparatus can reduce delay between the point in time at which theleading picture is decoded and the point in time at which the decodedpicture is displayed (that is, the delay between the start of thedecoding of the content to the displaying of the content) by decodingand displaying only forward reference pictures (I picture, P picture,forward reference B picture). Still further, the display apparatus maypurposely ignore the reference relationship between pictures, andcoarsely decode all B and P pictures as forward reference pictures, andthen perform normal decoding as the number of pictures received overtime increases.

Autonomous Driving

When transmitting and receiving still image or video data such as two-or three-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., containingthe reception terminal is mobile, the reception terminal may seamlesslyreceive and perform decoding while switching between base stations amongbase stations ex 106 through ex 110 by transmitting informationindicating the position of the reception terminal. Moreover, inaccordance with the selection made by the user, the situation of theuser, and/or the bandwidth of the connection, the reception terminal maydynamically select to what extent the metadata is received, or to whatextent the map information, for example, is updated.

In content providing system ex 100, the client may receive, decode, andreproduce, in real time, encoded information transmitted by the user.

Streaming of Individual Content

In content providing system ex 100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, and short content from anindividual are also possible. Such content from individuals is likely tofurther increase in popularity. The server may first perform editingprocessing on the content before the encoding processing, in order torefine the individual content. This may be achieved using the followingconfiguration, for example.

In real time while capturing video or image content, or after thecontent has been captured and accumulated, the server performsrecognition processing based on the raw data or encoded data, such ascapture error processing, scene search processing, meaning analysis,and/or object detection processing. Then, based on the result of therecognition processing, the server - either when prompted orautomatically - edits the content, examples of which include: correctionsuch as focus and/or motion blur correction; removing low-priorityscenes such as scenes that are low in brightness compared to otherpictures, or out of focus; object edge adjustment; and color toneadjustment. The server encodes the edited data based on the result ofthe editing. It is known that excessively long videos tend to receivefewer views. Accordingly, in order to keep the content within a specificlength that scales with the length of the original video, the servermay, in addition to the low-priority scenes described above,automatically clip out scenes with low movement, based on an imageprocessing result. Alternatively, the server may generate and encode avideo digest based on a result of an analysis of the meaning of a scene.

There may be instances in which individual content may include contentthat infringes a copyright, moral right, portrait rights, etc. Suchinstance may lead to an unfavorable situation for the creator, such aswhen content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Further, the server may be configured torecognize the faces of people other than a registered person in imagesto be encoded, and when such faces appear in an image, may apply amosaic filter, for example, to the face of the person. Alternatively, aspre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background to be processed. The server may process the specifiedregion by, for example, replacing the region with a different image, orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the person’s head region may bereplaced with another image as the person moves.

Since there is a demand for real-time viewing of content produced byindividuals, which tends to be small in data size, the decoder may firstreceive the base layer as the highest priority, and perform decoding andreproduction, although this may differ depending on bandwidth. When thecontent is reproduced two or more times, such as when the decoderreceives the enhancement layer during decoding and reproduction of thebase layer, and loops the reproduction, the decoder may reproduce a highimage quality video including the enhancement layer. If the stream isencoded using such scalable encoding, the video may be low quality whenin an unselected state or at the start of the video, but it can offer anexperience in which the image quality of the stream progressivelyincreases in an intelligent manner. This is not limited to just scalableencoding; the same experience can be offered by configuring a singlestream from a low quality stream reproduced for the first time and asecond stream encoded using the first stream as a reference.

Other Implementation and Application Examples

The encoding and decoding may be performed by LSI (large scaleintegration circuitry) ex 500 (see FIG. 68 ), which is typicallyincluded in each terminal. LSI ex 500 may be configured of a single chipor a plurality of chips. Software for encoding and decoding movingpictures may be integrated into some type of a recording medium (such asa CD-ROM, a flexible disk, or a hard disk) that is readable by, forexample, computer ex 111, and the encoding and decoding may be performedusing the software. Furthermore, when smartphone ex 115 is equipped witha camera, the video data obtained by the camera may be transmitted. Inthis case, the video data may be coded by LSI ex 500 included insmartphone ex 115.

Note that LSI ex 500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content, or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content, or when the terminalis not capable of executing a specific service, the terminal may firstdownload a codec or application software and then obtain and reproducethe content.

Aside from the example of content providing system ex 100 that usesinternet ex 101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast, whereas unicast is easier with contentproviding system ex 100.

Hardware Configuration

FIG. 73 illustrates further details of smartphone ex 115 shown in FIG.68 . FIG. 74 illustrates a configuration example of smartphone ex 115.Smartphone ex 115 includes antenna ex 450 for transmitting and receivingradio waves to and from base station ex 110, camera ex 465 capable ofcapturing video and still images, and display ex 458 that displaysdecoded data, such as video captured by camera ex 465 and video receivedby antenna ex 450. Smartphone ex 115 further includes user interface ex466 such as a touch panel, audio output unit ex 457 such as a speakerfor outputting speech or other audio, audio input unit ex 456 such as amicrophone for audio input, memory ex 467 capable of storing decodeddata such as captured video or still images, recorded audio, receivedvideo or still images, and mail, as well as decoded data, and slot ex464 which is an interface for Subscriber Identity Module (SIM) ex 468for authorizing access to a network and various data. Note that externalmemory may be used instead of memory ex 467.

Main controller ex 460, which may comprehensively control display ex 458and user interface ex 466, power supply circuit ex461, user interfaceinput controller ex462, video signal processor ex 455, camera interfaceex 463, display controller ex 459, modulator/demodulator ex 452,multiplexer/demultiplexer ex 453, audio signal processor ex 454, slot ex464, and memory ex 467 are connected via bus ex 470.

When the user turns on the power button of power supply circuit ex 461,smartphone ex 115 is powered on into an operable state, and eachcomponent is supplied with power from a battery pack.

Smartphone ex 115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex 460,which includes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex 456 is converted into a digital audiosignal by audio signal processor ex 454, to which spread spectrumprocessing is applied by modulator/demodulator ex 452 and digital-analogconversion, and frequency conversion processing is applied bytransmitter/receiver ex 451, and the resulting signal is transmitted viaantenna ex 450. The received data is amplified, frequency converted, andanalog-digital converted, inverse spread spectrum processed bymodulator/demodulator ex 452, converted into an analog audio signal byaudio signal processor ex 454, and then output from audio output unit ex457. In data transmission mode, text, still-image, or video data may betransmitted under control of main controller ex 460 via user interfaceinput controller ex462 based on operation of user interface ex 466 ofthe main body, for example. Similar transmission and receptionprocessing is performed. In data transmission mode, when sending avideo, still image, or video and audio, video signal processor ex 455compression encodes, via the moving picture encoding method described inthe above embodiments, a video signal stored in memory ex 467 or a videosignal input from camera ex 465, and transmits the encoded video data tomultiplexer/demultiplexer ex 453. Audio signal processor ex 454 encodesan audio signal recorded by audio input unit ex 456 while camera ex 465is capturing a video or still image, and transmits the encoded audiodata to multiplexer/demultiplexer ex 453. Multiplexer/demultiplexer ex453 multiplexes the encoded video data and encoded audio data using adetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex 452 andtransmitter/receiver ex 451, and transmits the result via antenna ex450. The determined scheme may be predetermined.

When video appended in an email or a chat, or a video linked from a webpage, is received, for example, in order to decode the multiplexed datareceived via antenna ex 450, multiplexer/demultiplexer ex 453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex 455 via synchronous busex 470, and supplies the encoded audio data to audio signal processor ex454 via synchronous bus ex 470. Video signal processor ex 455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex 458 via display controller ex 459. Audio signalprocessor ex 454 decodes the audio signal and outputs audio from audiooutput unit ex 457. Since real-time streaming is becoming increasinglypopular, there may be instances in which reproduction of the audio maybe socially inappropriate, depending on the user’s environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, may bepreferable; audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex 115 was used in the above example, otherimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. In thedescription of the digital broadcasting system, an example is given inwhich multiplexed data obtained as a result of video data beingmultiplexed with audio data is received or transmitted. The multiplexeddata, however, may be video data multiplexed with data other than audiodata, such as text data related to the video. Further, the video dataitself rather than multiplexed data may be received or transmitted.

Although main controller ex 460 including a CPU is described ascontrolling the encoding or decoding processes, various terminals ofteninclude Graphics Processing Units (GPUs). Accordingly, a configurationis acceptable in which a large area is processed at once by making useof the performance ability of the GPU via memory shared by the CPU andGPU, or memory including an address that is managed so as to allowcommon usage by the CPU and GPU. This makes it possible to shortenencoding time, maintain the real-time nature of the stream, and reducedelay. In particular, processing relating to motion estimation,deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of pictures, for example, all at once.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, digital video cameras, teleconferencingsystems, electronic mirrors, etc.

What is claimed is:
 1. A non-transitory computer readable medium storinga bitstream, the bitstream including information according to which adecoder performs an inverse transform process and an inversequantization process on a current block, wherein in the inversetransform process: the inverse transform process selectively includes aninverse orthogonal transform and selectively includes an inversesecondary transform, the inverse orthogonal transform being performed onprimary transform coefficients of the current block and the inversesecondary transform being performed on secondary transform coefficientsof the current block, and in the inverse quantization process: either afirst inverse quantization process or a second inverse quantizationprocess is performed on the current block based on the inverse transformprocess to be performed on the current block, wherein the first inversequantization process is performed on the current block in both of afirst case where both the inverse orthogonal transform and the inversesecondary transform are skipped for the current block and a second casewhere both the inverse orthogonal transform and the inverse secondarytransform are performed on the current block, the first inversequantization process not using an inverse quantization matrix, and thesecond inverse quantization process is performed on the current block ina case where the inverse orthogonal transform is performed and theinverse secondary transform is not performed on the current block, thesecond inverse quantization process using a first inverse quantizationmatrix, the first inverse quantization matrix generated by performing anup-conversion and a down-conversion on a second inverse quantizationmatrix.